To solve the problems of high labor intensity and long working time of artificial overthrowing of feed in the pasture, an autonomous navigation system based on LiDAR for synchronous positioning and map building was designed to realize robot navigation and grass turning in pasture environment. The autonomous navigation system platform perceived the pasture environment through LiDAR, a ranch environment map was constructed by using Cartographer algorithm loaded with odometer information, the AMCL algorithm was used which did not load the odometer information to achieve robot positioning, and Dijkstra algorithm was used to plan the robot to overthrow the grass work path. The experiment showed that when constructing the ranch environment map, the maximum deviation of the robot loading odometer information was lower than that of the map when the odometer information was loaded, which was 0.02m and 0.14m, respectively, and the maximum value of the horizontal and vertical deviation and the maximum heading declination angle were less than 0.04m, 0.10m and 11° when the positioning and navigation of the robot were realized, and the navigation accuracy was higher than the value when loading the odometer information. All the results showed that the navigation accuracy can meet the requirements of overthrowing grass operations in a pasture environment.