Aimed at the difficulty of selecting parameters in bistable stochastic resonance system, based on the RungeKutta algorithm, a system parameters adjustment method is put forward in taking the fixed potential barrier height as conditions of constraint in this paper. First, according to the formula of output signal's SNR, the constraint conditions of parameters a,b are obtained. Then, the value of a is rapidly searched under conditions of constraint, thus making the output spectrum amplitude increased again. Finally, the maximum SNR of the output signal corresponding to the input signal can be obtained. The simulation results show that this method can effectively suppress the low frequency interference signals in detecting high frequency weak signals, and the output signal's SNR is increased by on average compared to that of traditional methods with no constraint conditions.