Numerical modeling is used to obtain insight into the details of the effect of back contact barrier height (φb) on the dark current density-voltage characteristics of CdS/CdTe solar cell. And relation between the roll-over and the barrier height is obtained. Analytic simulations are fitted to the measured current density-voltage curve in a temperature range from 220 to 300 K. And the influence of barrier height on J-V of the CdS/CdTe thin film solar cell with Cu/Mo back contact fitted parameters is discussed. The equation between back contact barrier height (φb) and the reverse saturation current density (Jb0) is revised and the experimental data are consistent with the simulation results very well.