In high precision PN code ranging systems, HPA is an important component. However HPA introduces nonlinear distortion. As a result, it decreases the ranging performance. The PN code ranging error caused by the nonlinearity of HPA is studied, by means of theoretical deduction and numerical simulation. Quantitative relation of ranging error and HPA type, HPA output back-off, code chip waveform parameter is employed. The research result provides important suggestion for the choice of HPA type, the reservation of HPA power and the design of PN code waveform.