Area coverage of directional sensor networks (DSNs) has been a research hotspot in recent years. This paper studies the relationship between VORONOI cell and corresponding virtual sensing circle (the circle with its location as center and sensing radius as radius), according to which it firstly ascertains the possible working direction to maximize coverage ratio in each of VORONOI cells. Then, in order to decrease overlap coverage between neighbor nodes, it adjusts the direction of node with the maximum overlap area, which is changed to the cell vertex with the minimum overlap coverage area. Finally, in order to avoid invalid coverage ratio, the directions of sensors close to the overall sensing field boundary are readjusted. Simulation results proved that this algorithm could improve the valid coverage area and decrease the invalid coverage ratio.