Entangled photon reach a HOM interferometer through two different paths, and second-order coherence procedureat HOM interferometer can performance a measurement with accuracy of several femtoseconds of the time difference of arrivalbetween the two paths.Based on this principle, a quantum positioning system is constructed.With the simultaneous second-orderquantum coherence measurements in four channels, the four dimensional space-time coordinates of user in a coordinate system couldbe accurate defined.The principle of positioning and clock synchronization based on second-order quantum coherence of entanglesphoton pairs and a preliminary scheme of satellite-based quantum positioning system is presented in this paper.