As the desilicating agent of sodium aluminate solution calcium oxide(CaO)is rational though thermomechanical analysis.The results showed desilication rate is increased with CaO addition,temperature increase and time extension. The optimized technological conditions for the deep desilication in sodium aluminate solution are as follows: the amount of CaO added is 4g/L, temperature is 85℃,and desilication duration time is 2h.In the experiment desilication rate is 98.52% and the surplus Si in sodium aluminate solution is bellow 0.50mg/L.