Joint is among the most important factors in understanding and estimating the mechanical behavior of a rock mass. The difference of the strength, deformation characteristic of joint will lead to different strength and deformation of rock mass. The direct shear test is very popular to test the strength of joint owing to its simplicity. In order to study the three dimensional characteristic of joint, the numerical simulation software FLAC3D is used to build the calculation model of direct shear test under both loads in normal and shear direction. Deformation and mechanical response of the joint are analyzed, showing that, (1) relationship between shear strength and normal stress meets the linear Mohr-Coulomb criterion, the results are similar with that from the laboratory test; (2) the distribution of stress on the joint increases from the shear loading side to the other; and with the increase of normal stress, the distribution of maximum shear stress does not change much. The analysis results can give some guidance for the real practice; (3) the result from the numerical modeling method is close to that from the laboratory test, which confirms the correctness of the numerical method.