BeiDou navigation satellite system transmits triple-frequency signals which are benefit for the fast and accurate fixation of carrier phase integer ambiguity. Traditional TCAR(Three Carrier Ambiguity Resolution) method based on geometry-free model finds the suitable combination coefficients of carrier phase and pseudo-range observations by using traversal integer search method, which makes the higher noise level and the lower success reliability. In the analysis of the error characteristics of the pseudo-range observations, the weighted combined noise level was defined and a new procedure within its constrains to select the optimal combination coefficients was introduced. With using Hatch filter to improve the real-time estimation accuracy of ionospheric delay, the integer ambiguity of three linearly independent combination coefficients was fixed successfully, thus the basic integer ambiguities were determined. Finally, the performances of the improved TCAR are showed both in short-baseline and long-baseline condition: compared with traditional TCAR method, the total noise level has decreased by 20% for extra-wide lane and wide lane; the fixation success rate of ambiguity has improved about 10%~18%; the success reliability of basic ambiguities has achieved 90% with 30 seconds epochs smoothing.