The method of crucible rotating oscillation damping was employed to measure the kinematic viscosity of magnesium melt and the curve of viscosity v versus temperature T from 935 K to 1190 K was obtained. It is exponential increase (decrease) law of viscosity with the temperature during heating and cooling process; Besides, based on the physical model for evolution behavior of atomic cluster in liquid structure, the main structural information of magnesium melt in this temperature interval — the curve of size d of atomic cluster versus temperature T was obtained; By analyzing the experimental and calculated data, it is found that both kinematic viscosity and size of atomic cluster of magnesium melt are monodrome function of the temperature and the relation between them is linear function, i.e., v=v0 + K·d(T). This relation reveals the change characteristic of viscosity for magnesium melt microstructure, which presents a new way for calculating kinematic viscosity of metal melt and understanding the micro-nature deeply.