The change of full lifecycle performances of magnetic greases from the initial state to the steady state until the dead end in seawater was investigated by using the magnetic grease seal test bed.By analyzing the dispersant,magnetic coated particles, and the value and oil separation of loading fluid by the methods of SEM,TEM and differential thermal analysis,the change process of magnetic greases was researched to find out the law of change of magnetic greases and the criterion of faults prediction of the magnetic greases.The results show that crosslinking hardening is the main reason to lead to the invalidation of magnetic greases.When the crosslinking hardening happens,the oil separation of loading fluid is increased and the carrying capacity is weakened,magnetic coated particles disperse sparsely and trend to diffusion.But there is no occurrence of oxidation reactions in magnetic particles,and the shape of dispersants is remained in good condition.