Combining nonequilibrium Green's functions and first-principles quantum transport calculations in density-functional theory, we investigate the effect of biaxial strain on the leakage current of BaTiO3 ferroelectric thin film. The results show that the compressive strain can effectively reduce the leakage current of ferroelectric thin film. Especially when the compressive strain is 4%, the leakage current will be reduced by nearly 10 times that of strain-free case. By calculating the transmission coefficient and the density of states, we find that the transmission probability of ferroelectric tunnel junction with compressive strain is smaller than that with tensile strain. Moreover, we find that the valence band shifts toward the lower energy zone while the conduction band moves toward the high energy zone, which leads to the enlarged energy band gap, thereby reducing the leakage current. Our study suggestes a suitable way to reduce the ferroelectric thin film leakage current and improve the performance of ferroelectric thin film and its relevant ferroelectric memory.