The relationship between the amplitude of the control signal and the barrier height of the bistable system is analyzed. The method of detecting weak periodic signal is proposed using additional control signal constituted stochastic resonance (SR) driven by two-frequency signals. The theoretical analysis showed that adjusting the amplitude of the control signal can change the barrier height of the bistable system and purposely produce stochastic resonance or make stochastic resonance more intense. The simulation and experiment results showed that the method is feasible. An effective method is provided to detect the weak periodic signal in the application of incipient fault diagnosis in machine.