Aiming at the problem of poor response of piezoelectric cantilever in low frequency region, a method to optimize the centrifugal distance of the magnet at the end of the cantilever is proposed based on self-tuning stochastic resonance. Firstly, the dynamic equation of end magnet is analyzed and deduced. Then the optimization function of self-tuning stochastic resonance frequency and rotation frequency is established based on the Kramers escape rate, and the optimal centrifugal distance matching mechanism is obtained. Finally, the optimal centrifugal distance is obtained by using the optimal centrifugal distance matching mechanism, and the displacement, velocity and voltage responses of the piezoelectric cantilever under different centrifugal distances are compared. The results show that when the centrifugal distance reaches the optimal value, in a certain frequency range, the stochastic resonance frequency follows the rotation frequency, the stochastic resonance phenomenon can occur continuously, and its effective response frequency band is extended to 30~50 rad/s, and the ratio of broadening the frequency band is about 40%, and the energy harvesting performance is effectively improved.