If diatomite is made into diatomite/molecular sieve composites, its specific surface area and adsorption capacity will be significantly improved. In this paper, diatomite/aluminum phosphate molecular sieve composites were prepared by a series of combined treatment processes of washing, sintering and acid hydrothermal treatment, and the feasibility of forming aluminum phosphate molecular sieve was verified by adding aluminum source, and the microstructure evolution behavior and pore structure change law during the formation of high-quality diatomite were discussed. The results show that the pore structure of diatomite includes macroporous, mesoporous and a small amount of microporous structure. Sintering at 500 ℃ dredge the holes of diatomite shell, but too high sintering temperature lead to the collapse of tubular structure. The aluminum phosphate molecular sieves with mesoporous structure are synthesized by acidic hydrothermal treatment. With the addition of aluminum source, the content of aluminum phosphate molecular sieves in diatomite/molecular sieve composites increases. When the aluminum source is 1.5 times of aluminum content in diatomite, the specific surface area and adsorption performance reach the maximum.