Abstract: This study aimed to improve the efficiency of map building for mobile robots in an unknown environment.Thus, a cooperative mapping method for multiple mobile robots via edge gradient algorithm is presented in this study.The unknown environment is divided into four regions, and different search tasks are assigned to the multiple mobile robot system by the distributed task allocation method, which can effectively prevent multiple mobile robots from falling into concave obstacle areas.The mobile robot can have a large field of view when moving away from obstacles and a small field of view when approaching obstacles.The global map of the unknown environment is constructed by collecting the relative coordinate information of obstacles by moving around them.Therefore, the obtained map-building data are relatively accurate.The convergence analysis of the edge gradient algorithm is presented.Finally, multiple groups of simulation experiments verified that the proposed method can be used to efficiently build a complete map of the unknown environment.