Abstract: The change of water content is one of the key factors affecting the stability of loess engineering.In order to establish the relationship between the water content and the stability of soil nailing, through triaxial compression test the paper investigated the variation of loess strength index c and φ when the water content changed, discussed the relationship between the soil strength attenuation and water content. Analysis and discussion were conducted for the influence of water content on the failure mode of soil nailing support and the variation of stability by using the theory of limit equilibrium, it was put forward that the occurrence sequence of 3 failure modes of soil nailing support was related to the water content and the sensibility of different failure modes to the moisture was different. It was considered that when the water content of the foundation pit soil is about 23.5%, the soil nailing support may start to destroy.