Qi is active and pertains to yang while blood is static and pertains to yin. So the relationship between qi and blood can be understood according to the relationship between yin and yang. In TCM the relationship between qi and blood is generalized as "qi is the marshal of blood and blood is the mother of qi". Here "marshal" means governing and "mother" means source and foundation. Since qi pertains to yang, it can govern the circulation of blood; because blood pertains to yin, it is the source for qi-transformation. However, the relationship between qi and blood is not so simple as mentioned above.

The effect of qi on blood is mainly demonstrated in three aspects, i.e. qi producing blood, qi promoting the circulation of blood and qi controlling blood.

Qi promotes the production of blood in various ways. In terms of the composition, the nutrient qi is the main component of blood, indicating that the nutrient qi produces blood. In terms of the transformation of blood, the production of blood depends on @transformation. The material needed for the production of blood is the food nutrient transformed and absorbed by the spleen and the stomach. 

The normal functions of the spleen and the stomach are directly related to spleen-qi and stomach-qi. If spleen-qi and stomach-qi are vigorous, blood-producing function will be vigorous too. If spleen-qi and stomach-qi are deficient, blood-producing function will be weakened. In fact the transformation of the food nutrients into blood still needs the transformation of other visceral qi. 

For example, only when the food nutrients has combined with kidney-essence can the process of transforming the nutrients into blood be accomplished; only when blood trans- formed from the food nutrients and the kidney-essence has been processed by the transforming activity of heart-qi and lung-qi, especially heart-qi, can blood become red. If the functions of the spleen and the stomach are weak due to qi deficiency or if the transforming activity of visceral qi becomes weak, the normal process of blood transformation will be affected, leading to blood deficiency.

Blood depends on the propelling function of qi to circulate. That is why TCM holds that "normal flow of qi ensures normal circulation of blood, stagnation of qi leads stasis of blood". In terms of visceral functions, heart-qi is the primary motivation of blood circulation; lung-qi assists the heart to propel blood to circulate; liver-qi promotes the circulation of blood. If qi is too weak to propel blood, blood will flow slowly; if qi activity is obstructed, blood will become stagnant; if qi activity is in disorder, blood will flow abnormally.

Qi controlling blood means that qi directs blood to circulate inside the vessels and prevents it from flowing out of the vessels. The kind of qi that can control blood and direct it to flow inside the vessels is spleen-qi. That is why TCM holds that "the spleen commands blood". If qi fails to control blood due to deficiency, blood will flow out of the vessels, leading to bleeding.

The effect of blood on qi is demonstrated in two aspects: carrying qi and producing qi.

Blood pertains to yin and is static, so it keeps on flowing inside. Qi pertains to yang and is active, so it tends to move to the outside. When qi and blood have combined with each other, blood has acquired a motivation to move and qi has obtained a carrier to attach to. That is why it is said that blood can carry qi. That is to say that only when qi has attached itself to blood can it avoid dispersion and loss. Clinically massive hemorrhage is usually accompanied by loss of qi. Therapeutically, apart from using the therapy for supplementing blood and stopping hemorrhage, other therapeutic methods for supplementing qi and stopping prostration must be resorted to.

Qi and blood, pertaining to yin and yang respectively, can transform into each other and produce each other. The primordial qi is produced by the congenital essence in the kidney and the food nutrients transformed by the spleen and the stomach. The normal functions of these organs all depend on nutrients provided by blood flowing in the vessels, and so do the other viscera and meridians. Thus the production of qi by blood is accomplished through its provision of nutrients for the viscera and meridians.