At long baseline, for multipath and ionospheric residual bias, classical CIR can get wrong ambiguity resolution at some epoch, and requires a large search area on basic carrier. In this research, ambiguity errors of CIR were analyzed, and an approach to improved CIR based on carrier phase smoothing pseudorange and eliminating ionosphere delay is presented and errors variance was analyzed. Finally, CIR and improved CIR were compared at both short and long baseline by compass measured datum. The result shows that improved CIR can obtain correct double difference extra wide lane ambiguity and wide lane ambiguity on one epoch, and reduce the search area on basic carrier ambiguity. 