In order to improve the impermeability and crack resistance ability of cement mortar, a new type of cement mortar material was developed in this paper. Through the preparation of bentonite and basalt fiber modified cement mortar with different content, the impermeability and crack resistance were tested, and the micro mechanism of cement mortar was analyzed. The results show that the addition of bentonite and basalt fiber enhances the impermeability and crack resistance of cement mortar. When 4% (mass fraction) bentonite and 0.4% (mass fraction) basalt fiber are mixed, the impermeability pressure of cement mortar is the highest, which increases by 61.11% compared with the group without bentonite and basalt fiber, and the impermeability grade is P8. At the same time, the crack reduction factor of cement mortar mixed with bentonite and basalt fiber reaches more than 80%, the crack resistance grade belongs to grade I, and the characteristics of cracks are "few, fine and short". Mixing bentonite and basalt fiber improves the compactness of cement mortar and reduces cracks and holes. The addition of bentonite and basalt fiber does not change the type of hydration products of cement mortar, but reduces the crystallinity of calcium hydroxide and promotes the formation of calcium silicate hydrate gel.