Under the alkaline condition, the synthesis of mesoporous molecular sieves MCM-41 had been accomplished successfully in a hydrothermal system using sodium silicate as the source of silicon and surfactant C16H33(CH3)3NBr as structural template. The technique of X-ray diffraction was used to identify the effects of the synthesis pH condition, the composition of gel (surfactant/SiO2, H2O/SiO2) and treating conditions of gel (aging time, crystallizing temperature, crystallizing time, calcined temperature) on the crystal structure of MCM-41. The results show that the synthesis conditions for getting suitable mesoporous molecular sieves MCM-41 are pH=10.5-12.5, surfactant/SiO2=0.05-0.7, H2O/SiO2=40-200, aging time as long as possible, crystallizing temperature 70°C-100°C, crystallizing time 24 hours and calcined temperature 540°C-740°C.