In order to overcome the limitation of the traditional bridge detection method, under the background of the unmanned aerial vehicle detection bridge, taking into account the signal without GPS, the information acquisition process and the grid method are combined to establish an environmental model, extremely covered the bottom of the bridge. In the path planning, most of the algorithms can only plan the shortest path, and the algorithm is complex, requires a lot of storage space, and it is difficult to carry out the whole area coverage path planning. Now the unit decomposition method and the two-point search strategy are proposed and applied in this context, so the algorithm has the advantages of simple computation and covering intelligence, It has great potential in the coverage path planning. Simulation experiments show that it can achieve the whole area coverage under the conditions of low power consumption.