Aiming at the characteristics of synchronous grouting and filling in water-rich and permeable stratum, the impact imaging method is applied to detect the filling state behind the shield tunnel wall. By the analysis of the reflection of shock elastic wave and its regional response characteristics, the impact response intensity of measuring points is obtained based on fast Fourier transform, and the spatial distribution cloud chart of grouting filling degree behind the shield tunnel wall is established by three-dimensional imaging. On this basis, the probability density function and risk evolution function of waveform distribution and impact response strength in the sample space of detection engineering data are established to quantitatively evaluate the filling state and risk of each survey area and line respectively; and a comprehensive evaluation system for the filling state behind the synchronous grouting wall of shield tunnel is established by integrating the probability density function in the corresponding risk area. The applicability of this method is verified by the engineering case.