The effect of the shearing velocity on filled joints is significant for the safety and stability of engineering rock mass under dynamic loads. To study the effect of the shearing velocity on shear mechanical properties of filled joints, sands were used as the filled material and the granite was used as joint wall. By using the RMT–150C servo-testing system, direct shear tests were conducted on filled joints to investigate the effects of normal stress, shearing velocity and filled thickness on shear mechanical properties. Experimental results show that the shear stress-displacement curve of the filled joint belongs to the yield shear type, and it can be further divided into three phases: elastic stage, transitional stage and slip stage. At the slip stage, the shear stress continually increased with increasing the shear displacement, and the increase amplitude was related to the normal stress. With the rapid growth of the shear rate, the shear strength and frictional angle increased slightly. The shear stress-displacement curve of the elastic phase was fitted by a hyperbolic form to study its non-linear process and the fitting result turned out to be good. Two new parameters, namely the initial stiffness and stiffness influence coefficient, were defined to describe shear deformation characteristics of the joint. Experimental results show that the initial stiffness increased sharply with increasing the shearing velocity to a high value. As the normal stress increased, the initial stiffness increased linearly, while the stiffness influence coefficient decreased obviously. Moreover, the effects of filled thickness on these two parameters were dependent on the normal stress. For the planar filled joint without roughness, both of the shearing velocity and filling thickness obviously have greater influence on deformation characteristics of the joint than on shear strength.