By analysing DV-Hop localization algorithm, for the larger error of average hop distance in the DV-Hop localization algorithm, we proposed a kind of localization algorithm for nodes in underwater sensor network based on average hop distance. The algorithm improves calculation average hop distance. First, the anchor node uses the boundary anchor nodes and its one-hop neighbors of anchor node to calculate average hop distance. Second,the unknown node receives broadcasting package including average hop distance from each anchor node, and then according to the hop-numbers to each anchor node with weight calculates the final average hop distance. Simulation results show that after two improvement the algorithm is superior to the traditional DV-Hop localization algorithm, and improves the location accuracy.