Abstract: The sluice built on the soft soil foundation is prone to problems such as uneven foundation settlement and seepage deformation, which will induce disasters such as the sluice floor void. The existing soft foundation sluice floor vacancy dynamics diagnosis method can identify the void range. However, the sensitivity of the basic modal parameters (natural frequency and mode coefficient of the measuring point) to the sluice floor vacancy needs to be further improved. Therefore, the effect of different model parameters and their derivatives on the sluice floor vacancy needs to be further improved. To explore the influencing laws of different model parameters and their derivative quantities on the sluice floor vacancy, it is of great significance to determine the more sensitive characteristic quantities of venting dynamics of the sluice floor. The modal flexibility, which is more sensitive to structural damage, is taken as the sensitive characteristic of sluice floor void dynamics, and the mathematic model of sluice floor void description is established. The mathematical proxy model of response surface between sluice floor void control parameters and modal parameters (modal flexibility) is improved based on the change rate of the first two order modal flexibility of each measuring point. The relative deviation between the modal parameters (modal flexibility) of the sluice finite element model under corresponding working conditions and the modal parameters (modal flexibility) of the response surface mathematical model is taken as the objective function, and the sluice floor void parameter inversion is transformed into the solution of the objective function. The results show that the relative error between the inversion results and the actual void range is significantly reduced by taking three typical void conditions as examples. The model improves the accuracy of the inversion of sluice floor void and provides a reliable method for the detection and diagnosis of sluice floor void on soft foundation.