Abstract: This paper investigates the phenomenon of stochastic resonance of an over-damped second-order linear system, whose intrinsic frequency and the driving signal frequency is perturbed by colored noise. Based on linear-system theory and the correlation deletion method, the explicit expression of the output amplitude gain (OAG) of the system is obtained. It is shown that the OAG is a non-monotonic function of the strength, the correlation rate of the colored noise, and the frequency of the driving signal. By choosing appropriate parameters of the noise and the system, the OAG of the noisy system can be larger than that of the noise-free system, so the OAG can be increased by changed the parameters of the noise the system.