Blood clots during menstruation indicate blood stasis. Cold clotting, Qi stagnation, and Qi deficiency may all lead to blood stasis, which manifests itself as a blood clot during menstruation. However, the amount of blood clots and the time when they appear are used to determine exactly which condition is causing them. The first menstrual period with blood clots is due to the presence of cold in the body, blood condenses when it encounters cold, but it moves when it gets warm. When Qi stagnation causes menstrual blood clots, the time of appearance is variable and the amount is sometimes variable, mainly because of the characteristic of Qi gathering and dispersing at times, when Qi is clear, the menstrual blood is also clear and there is no blood clot, while when Qi is stagnant, Qi does not work, the blood does not work and there is a blood clot. In contrast, clots during menstruation caused by Qi deficiency generally last for a longer period of time, some even last for the whole course of menstruation, and the clots are obviously aggravated after exertion, accompanied by long menstrual cycles and high menstrual volume. The last type must be treated with clinical caution. Avoiding strain during menstruation is the first priority, while paying attention to protection against cold and warmth and ensuring sleep. There is also a condition that after treatment, a large amount of blood clots are discharged during menstruation and the color, quality and cycle of menstruation return to normal in the next cycle, which is a sign of proper treatment and physical improvement.