An improved bipartition theory for light-ion transport is presented. The improved theory allows the use of accurate but more complex nuclear scattering cross sections and stopping powers in the Boltzmann transport equation, instead of the power function approximation of the nuclear scattering cross sections and the stopping powers used in earlier bipartion theory [Z.-M. Luo and S.-M. Wang, Phys. Rev. B 36, 1885 (1987)]. Furthermore, the theory is extended Tao treat the transport for obliquely incident ions. By the improved bipartition theory, the particle reflection coefficients and energy reflection coefficients, as well as energy distribution of reflected ions for cases of H, D, and He ions incident on C, Ni, Fe, Cu, W, and Au, have been calculated. The comparison of the present calculation results with available experimental data and the Monte Carlo data shows that the improved bipartition model for light ions is useful.The particle reflection coeflcient of ion RN: