In order to improve the operating and locating accuracy of intelligent equipment under special working environment (high radioactivity, high temperature, high pressure, boric acid and so on) in nuclear power plant. The nonlinear mathematical model of underwater binocular vision is established, considering both refraction effect and lens distortion. To achieve this, it is analyzed that the imaging principle of the boric acid underwater vision as well as the influence factors and presented that a kind of underwater binocular vision positioning method to unstructured environment. In order to verify the method, the comparison experiments are done in the air, common water and different concentrations of boric acid water. The experimental results show that different concentration of boric acid has little influence on the camera imaging refraction, and target attribute dimension calculated is close to actual value.