The N type properties of reflected bistable optical devices (RBODs) are studued by using the accuracy matrix formulas based on the principle of thin film optics. The relationship between δI 0、 δI r and δ, which are all the important parameters of RBODs, is plotted. The dispersive relations of ZnSe thin film are intoduced into the method to make the theoretical method self consistent. Finally, experimental result of a RBOD of nonlinear interference filter is given.