Abstract: In order to solve the problem of the lower success rate to fix ambiguity with CIR method when the carrier phase observation noise and pseudorange observation noise are quite large, an improved CIR method was proposed. The ordering and multi-time (inverse) paired Cholesky decomposition method were used to reduce the correlation of ambiguity float solution and covariance matrix with the least square method. And then the MAEVZ method was used to search the fixed integer ambiguity. Simulation results show that, when the pseudorange observation noise is 2.0 m and carrier phase observation noise is 0.03 cycle, the success rate of integer ambiguity resolution is below 5% with CIR method and it can't accurately fix integer ambiguity, however the success rate of integer ambiguity resolution is beyond 90% with the improved CIR method.