Abstract: The pulsars are the result of a massive star that has exhausted its nuclear fuel and undergone a core-collapse resulting in a supernova explosion. Its radius is roughly 10 km and mass near 1.4 solar. There are the very strong gravitational, electronic and magnetic fields for the pulsar. The pulsar might emit in the radio, infrared, visible, ultraviolet, X-ray and gamma-ray of the spectrum. Meanwhile, the navigation parameters for the spacecraft on the low earth orbit, deep space and interplanetary flight can, including the position, velocity, attitude and time, be determined highly-accurately by detecting the X-ray radiation of pulsars. And then the spacecrafts are able to flight and operate autonomously. Therefore, the potential of using the X-ray Pulsar Navigation （XPNAV） is very high. Firstly, the history of XPNAV is described briefly in this paper. Secondly, the basic principles, information flow charts and autonomous navigation algorithms are studied in detail as an main part. Moreover.the key techniques of XPNAV, including the all-sky surveying and data processing for the X-ray pulsars, pulse-arrival-time measuring and error correcting, X-ray detector and weak signal processing, establishment and maintenance of the space-time reference, and robust filtering of the autonomous information processing, are also presented. Finally, the essentiality and feasibility to study XPNAV are also shown in some detail.