In wireless channel system, co-site interferencewill cause the receiver's reception sensitivity to decline. Based on microwave photonics technology, according to the nonlinear characteristics of intensity modulated direct detection(IMDD) optical link, a radio frequency co-site interference suppression method is proposed. Firstly, the mathematical model of the output power of IMDD optical link is established, and the output power of interference signal and useful signal is described by mathematical equation. By making the output of interference signal zero, the solution of the equation is obtained, and the conditions of interference suppression are obtained. Then, through Matlab quantitative calculation, the curve of the output power of interference signals and useful signals in the link changing with the input interference signal power is obtained, the power output point of interference suppression is obtained, and the influence of half wave voltage on interference suppression is analyzed. The experimental results show that the suppression ratio of this method can reach -64.5 dB, and the output power of the useful signal is only lost by 6.4 dBm, which has excellent interference signal suppression ability.