The present application discloses a method and device for updating a map. The method for updating a map according to the present embodiment includes: in a process of movement of a robot, when it is detected that an actual environment is different from an environment that is indicated by a global map that has already been established, starting up map updating, and establishing an initial local map; determining a locating point according to acquired sensor data and the global map, and optimizing the initial local map according to the locating point, to obtain an optimized local map; and covering a corresponding area of the global map by using the optimized local map, to complete updating of the global map. The embodiments of the present application improve the locating accuracy, ensure the speed and efficiency of the map updating, and save time.