Camera coverage is an important basis of camera network initial configuration, optimal deployment and so on. Its precision and efficiency are the critical influences on the results of coverage analysis, which are very important to the application of large area camera coverage analysis, but many methods do not consider them. A new method to efficiently estimate camera coverage was proposed. Firstly, the geographic space was dispersed into grids. Secondly, the statuses of the four corners of each grid were computed. If the corner was covered by the camera, the status was denoted by using 1 or 0. So the status of the gird can be presented by the code which is either 0 or 1. Consequently there are 16 statuses to represent the status of a grid. Finally, if the code of the grid was not (0000) or (1111), the gird would be divided into four isometrical sub-girds until the subgirds were small enough or their codes were (0000) or (1111). According to the levels and statues of all grids, the whole camera coverage was estimated. Experimental results show that the proposed method can obtain more precise camera and can give consideration to both efficiency and accuracy.