A tangential function was introduced to describe the nonlinear light-electric current relationship of a photo-electric diode, then based on the rate equations of semiconductor laser and on the nonlinear function-equation mentioned above, the theoretical model on the bistable laser diode (BILD) was established, and the main properties of BILD were analyzed by using this model. The main performances of the BILD were discussed with its results from numerical analysis. Finally, according to the results from the numerical analysis, the ways to improve the response feature of BILD were also proposed.