In order to effectively solve the sensors nodes mobility difficult problem in the water, the paper presents a localization algorithm based on mobile nodes—MNLS(mobile nodes localization algorithm). The main reasons of nodes mobility are the waterflow and random noise. The algorithm is on the basis of the analysis of the existing relevant localization algorithms, we present the idea which firstly forecasts nodes' trajectory, then calculates the nodes' distances and coordinates. The algorithm is simulated by MATLAB, and the results show that compared MNLS with Chan algorithm. The single node's positioning accuracy and different speed nodes' precision are all improved. So it has an application value for the underwater sensor network localization.