On the basis of the investigation on the role of change of viscosity with radiation, we studied the relationship between viscosity and the properties of blood population. It was found that the viscosity depeneded on the concertration of blood cells. In fact, it concerned blood cells hematocrit and cells electrophoresis on the early period of radiation, especialy erythrocyte electrophorsis. During the sickness, it related to the change of the erythrocyte sedimentation rate. When the mice was irradiafed at 6 Gy, it was concern of erythrocyte defomation. But plasma viscosity is not main factor of blood viscosity.