In this paper, the influence of the types and addition dose of MgO expanding agent and the age of cement on expansion value and expansion performance of cement based material added with MgO expanding agent was systematically studied.The expansion characteristics of cement based material added with MgO expanding agent or calcium sulphoaluminate expanding agent were compared. The expansion of such material increases with the addition dose of MgO expanding agent and cement mortar age. During the test period, the expansion of cement based material increases continuously. The light-burned MgO expanding agent modified by CaO expanding agent is able to increase the 28d expansion of such material effectively. The temperature of calcination for the heavy-burned MgO expanding agent is higher than that of light-burned one, thus the heavy-burned MgO expanding agent has a rather dense structure with slow hydration rate and gives a small expansion of the cement based material at early age, showing an obvious expansion delay. The calcium sulphoaluminate expanding agent gives most expansion of the material in the early 28d and there is small expansion at middle and later age of the material.