Abstract: This paper introduces corrosion mechanics and impact factors to steel pipes in hydrostatic pressure test using seawater and mainly describes the process of seawater treatment. Research results show that an optimum approach for seawater treatment in pressure test is to filter and add chemical agents. Suspended substance will be less than 10 micron for its particle size and its content below 5 mg/L by selecting suitable filter. The solution oxygen will be reduced to below 0. 01 ppm and kill bacterium to slow pipe wall corrosion by using proper chemical agents such as deoxidant, bactericide and inhibitor. An example of hydrostatic pressure testing with seawater in the Libya W estern Pipeline is provided.