The conventional tightly coupled INS/GPS integrated navigation system uses GPS pseudorange/pseudorange rate as measurements. Usually GPS pseudorange rate can provide velocity information with cm/s level precision, while the measurements of carrier phase temporal difference can reach mm level precision without reference of receiver. This article analyze the theory of carrier phase temporal difference and apply it in INS/GPS integrated navigation system and use the state delay filter method to handle the measurements of carrier phase temporal difference in the design of filter, thus make the INS/GPS integrated navigation system reach a higher velocity precision.