By using FLUENT, a numerical simulation analysis is respectively conducted on conical, cylindrical and conical straight nozzles water jet flow field of which are currently widely used in industrial pipe high pressure jet descaling. By orthogonal experiments to the best jet nozzle type of flow field characteristics, its optimum structure size was gained. The results show that: the conical straight nozzles water jet flow field characteristics are the best, fluid velocity increases rapidly in the nozzles convergent section, uniform flow nuclear zone appears at the horizontal transition phase, in the radial direction the radial velocity without significant fluctuations is more conducive for descaling. When straight taper length L of the nozzle is 17 mm, the length l of the horizontal transition section is 6 mm, the nozzle diameter d is 1 mm and the contraction angle α is 16°, the effect of descaling is the best.