The invention discloses a tightly coupled INS/UWB integrated navigation system and method adopting fixed-interval CRTS smoothing. The navigation system comprises an inertial navigation system (INS), a UWB radio tag, UWB wireless reference nodes, a reference system and a data processing system, wherein the inertial navigation system (INS) and the UWB radio tag are arranged on shoes of a pedestrian; the UWB wireless reference nodes and the reference system are arranged at a set position; the inertial navigation system (INS), the UWB radio tag and the reference system are connected with the data processing system respectively; the data processing system comprises a local data fusion filter, a Cubature Kalman Filter (CKF), a pseudo-distance data processing module, an RTS smoothing module and an average filtering module. The tightly coupled INS/UWB integrated navigation system and method has the benefits that the possibility of introducing truncation errors due to omitting of higher terms of Taylor expansion in a conventional tightly coupled integrated navigation model is effectively decreased.