The interdiffusion behavior of Ti-Zr binary alloy in the β phase (950 to 1150 oC) was studied through the diffusion couples by EPMA. The interdiffusion coefficients of the Ti-Zr binary alloy were calculated by the Den Broeder method and modified by the Hall method in the concentration limits between 10-14 and 10-12 m2/s. The diffusion activation energy Q and frequency factor D0 were calculated. The results show that Q and D0 increase at first and then decrease with the increase of Zr concentration and a summit can be got at about 50at% Zr concentration. The impurity diffusion coefficients in concentration limits were calculated by Vignes-Birchenall method and they were compared with the interdiffusion coefficients determined by Hall modification method. It is found that their results are similar.