Abstract: The urban microtremor exploration technology is a method that detects urban underground structures by using the weak vibration of environment.The surface wave is dominant in the microtremor recordings, and the surface wave dispersion curve can be extracted by further analysis of the fretting signal, and the shear wave velocity can be obtained by inverting the dispersion curve.There is a contradiction among the scale of stratigraphic division, the calculation cost and solution stability.The more stratigraphic division layers, the more unknown parameters in the inversion process.Too much stratigraphic division will increase the computational overhead, aggravate the uncertainty of the equation, and make the inversion results inaccurate.In order to solve this problem, this paper proposes an improved algorithm based on geological unit by drawing on previous studies.When the convergence rate of inversion is low, the two adjacent units with small s-wave velocity difference are combined and the combined stratum participates in inversion.Through the analysis of numerical simulation and measured data, the improved inversion algorithm based on geological unit can reduce the uncertainty of the equation, obtain more stable solutions and reduce the computational overhead.