The low-frequency radiated sound field can be effectively controlled through the adaptive active control method in theory. However, its application in underwater radiated noise control is not wide. In the active control system, especially the multi-channel feedback system, the step size has a very tremendous influence on the performance of the adaptive filter. If the step size is set unreasonably, the calculation results will not converge. The appropriate step size varies from case to case. For simple cases, the empirical value can be adopted to set the step size. When the numerical difference between channels is large, and when the control physical quantity such as sound pressure changes greatly with time, an determined step length can t meet the control requirements. In particular, it is difficult to choose the step size when the accurate reference signal cannot be obtained. The application of adaptive active methods in underwater noise control is limited to some extent by this problem. To solve this problem, this essay carried out the research of Filtered-X Least Mean Squares (FxLMS) algorithm based on variable step size, and carried out the corresponding numerical analysis and pool experiment to verify the feasibility of applying to underwater noise control.