The effect of different organosilane coating amounts on the protective performance of aluminate cement mortar was studied. Using the contact angle tester, infrared spectrometer(FTIR), X ray diffractometer(XRD), and scanning electron microscope(SEM), the protective effect of organosilanes and the causes of the differences were characterized and analyzed. The results show that when using a one time coating method, the water absorption rate of the aluminate cement mortar decreases first and then trend to stable with the increase of the coating amount of silane. The water absorption rate decreases by more than 90%, which meets the specification requirements. After coating with silane, the contact angle of the mortar increases first and then decreases with the increase of the coating amount of silane, surface changes from hydrophilic to hydrophobic, and the contact angle reaches 14266° when the coating amount is 250g/m2. The penetration depth of silane increases first and then decreases with the increase of the coating amount, and the penetration depth can reach 1073mm when the coating amount is 250g/m2. The silane modified mortar is hydrolytically condensed on the inner wall of the pores to form a water repellent mesh silicone hydrophobic film layer, and no new crystals are formed.