Abstract: How to locate microseismic events accurately and efficiently is an important problem in microseismic monitoring.However, the traveltime-based linear inversion, a routine method for event locating, suffers from some problems such as shadow area and caustics during ray tracing in complex heterogeneous media and thus fails to obtain accurate ray paths.Additionally, local minima in travel time calculation are also an obstacle to accurate positioning.We propose a method to locate microseismic events based on an improved multi-stencils fast marching (MSFM) algorithm.The approach utilizes a spherical wave approximation algorithm to compute the travel times at grid points near the seismic source, followed by solving the Eikonal equation using MSFM to calculate travel times at the remaining grid points.Finally, a global search of event positions is conducted using the travel time difference as the objective function.The model test results show that the improved method proposed in this paper outperforms the Fast Moving Method (FMM) and conventional MSFM in travel time calculation, especially in the vicinity of the source.This method can also achieve accurate ray tracing and positioning in layered and complex velocity models.The application to Weiyuan shale gas field in the Sichuan Basin shows more accurate results of event positioning and fracture delineation compared to the Geiger method.