PN code ranging technique based on DSSS is widely used in satellite navigation, radar, and aerospace TT&C. The phase distortion introduced by RF link and cable multi-path will greatly affect the signal time delay of spread spectrum. The traditional definition of group delay is incapable of describing the holistic phase character of signal bandwidth, thus having difficulty in establishing relationship with the spread spectrum signal delay. To resolve these problems, a new group delay definition has been put forward, based on Taylor series expansion, which uses zero order group delay, linear group delay and parabolic group delay to describe phase distortion. The influence of the different order group delay on PN code ranging was analyzed and simulated. The results show that the parabolic group delay has greatest effect on PN code ranging.