Considering the low bearing capacity and large deformation of rubber sand as backfill material， a method involving the addition of polypropylene fibers（PPF） to rubber sand was employed to enhance its mechanical performance. A semi-dry mixing method for preparing polypropylene PPF reinforced rubber sand was proposed. Through 48 sets of consolidated undrained shear tests on PPF reinforced rubber sand， ordinary rubber sand， and pure sand samples， the influence of parameters such as PPF content and rubber content on the main mechanical deformation characteristics of PPF reinforced rubber sand was investigated. The results indicate that PPF fibers have a relatively small impact on the elastic modulus of rubber sand. PPF reinforced rubber sand exhibits a characteristic failure pattern of initial shear contraction followed by shear dilation， with a strain-hardening relationship between shear stress and axial strain. PPF fibers effectively enhance the internal friction angle and cohesion of rubber sand. The improvement in the failure shear stress of PPF reinforced rubber sand is significant with a maximum increase of up to three times.