The microscopic mechanism of low level laser irradiation (LLLI) mending rheology for blood is analyzed by the quantum theory. The results show that the laser can resolve the fibrin clot, so the property of blood rheology is improved, and some bonds of the cholesterol in blood are fractured by the low level laser (LLL). Hence the ratio of membrane cholesterol to membrane phosphatide of the red cell is reduced, and then the blood circulation can be improved. The clinical cured tests and some correlative test data can be explained by the theoretical analyses in this paper. The microscopic mechanism of low level laser irradiation (LLLI) mending rheology for blood is analyzed by the quantum theory. The results show that the laser can resolve the fibrin clot, so the property of blood rheology is improved, and some bonds of the cholesterol in The clinical cured tests and some correlative test data can be explained by the theoretical analyzes in this paper.