An online secondary path identification method is proposed based on the modified filtered-X least mean square (FXLMS) algorithm, which is applied in adaptive active control of structural vibration. The proposed algorithm can eliminate the perturbation between the active control process and secondary path modeling process, accelerate the convergence speed of the system, reduce the contribution of auxiliary noise to the residual vibration, and simplify the complexity of the algorithm. Active vibration control simulations are provided based on LABVIEW software. Compared with existing methods, the proposed method has superior performance in the convergence and effect of active vibration control. Finally, an active structural vibration control experiment is made on a simply supported beam using the proposed method to achieve good inhibitory effect of the beam′s vibration response. The results illustrate the effectiveness of the secondary path online modeling method for active control.