We choose a correlation function of chiral current to calculate the form factors f+Bπ(q2), f Bπ(q2) and the scalar form factor of f0(q2), thereby we can study the effect of leptonic mass on B0→π－l+ν l (l=e, μ, τ) decay. In this paper, we calculate the branching ratio of B0→π－l+ν l(l=e, μ, τ) decay for the first time, and find the leptonic mssses me and mμ may be ignored, but the heavy leptonic mass mτ may not be ignored and it can affect the branching ratio. The calculation results are consistent with the experimental data.