A large fault fracture zone with about 100 m wide exists in Wuyue Pumped Storage Power station of China, where the low-strength and highly-fractured granite severely restricts the stability of the underground powerhouse. However, no relevant exploration has been made on its lithology to ensure the safety of the upcoming construction. To overcome this insufficiency, we present the most recent researches on the strength and deformation of the local granite. The local rock samples were obtained through field sampling from the exploratory adit PD1, and its deformation and strength properties depending on environmental conditions was thoroughly investigated, by mean of experimental and theoretical analysis. Primary attention is given to the prediction and engineering guidance of the proposed model upon the mechanical parameters and shear strength when considering the more extensive environmental variables, namely, dry densities and confining pressures. Experimental results show that the failure of remoulded soils with completely decomposed granite is characterized by bulging deformation in the middle without a visible failure surface, along with significant “volume-contraction”. Also, the influence of environmental variables on mechanical parameters is different, in particular peak strength and elastic modulus present highly linear correlation with the confining pressure and dry density. Additionally, based on the measurements, the proposed universal function law upon mechanical parameters and shear strength depending on environmental variables, compare well with experimental results for practical purposes. Our conclusions are useful to capture the deformation and strength behaviour and then put forward corresponding measures for the poor surrounding rock mass, especially those being highly decomposed, where the Wuyue Pumped Storage Power station is to be built shortly.