Abstract: This paper studies the influences of sodium phosphate impurity on the seeded precipitation of sodium aluminate solution and its affecting mechanism ． The results show that sodium phosphate impurity increases the seeded precipitation rate of sodium aluminate solution and increase the product particle size when the concentration of sodium phosphate is less than 5g／L．Phosphates impurities can not significantly affect the Zeta potential of aluminum hydroxide in sodium aluminate solution．However，it can increase the surface tension of sodium aluminate solution．