Abstract: Fluctuating targets reduce the detection probability of radar such as stealth aircraft greatly. Traditional radar adopts non-coherent detection, but its detection performance is not good enough to counter such fluctuating targets nowadays. In response to the above problem, the coherent detection was applied to fluctuating targets to improve detection probability of radar. Swerling fluctuating target models, for example, it is derived based on multiple integral equations the detection probability formula of coherent detection for Swerling Ⅰ and Ⅲ fluctuating target models in this paper. Simulation results verified the accuracy of the theoretical derivation formula, and then compared the non-coherent detection, analyzed the relation of detection probability with false alarm probability and the number of integrated pulses, and the fluctuation loss of two detection methods for fluctuating targets is also calculated. According to the characteristics of fluctuating targets, by coherent detection, the radar detection probability will increase when select perfect fluctuating models and number of integrated pulses.