Abstract: Linear combination of the triple original carrier based on geometry-free(GF) and ionosphere-free(IF) can eliminate the first-order ionospheric-delay item and some other error terms influenced by geometric-distance between the satellite and station, thus it can be effectively applied to ambiguity-resolution for medium-long baseline. In this paper, the GF and the IF linear combination observations were studied and optimized for BDS long-baseline ambiguity resolution. Carrier and pseudorange observations were used to get the combination observation with minimum noise and based on GF and IF character, and considering that the ambiguity-correct carrier phase observation has lower noise compared with pseudorange observation, two carrier combinations with ambiguity-fixed and original carriers were applied to get the third optimal GF and IF combination with the minimum noise.Observations including all pseudoranges and carriers were applied in different weight according to their noises. Finally, real data of BDS triple frequencies were applied to verify the feasibility of model in the experiment.The result showed that the deviation of WL and NL float ambiguity resolutions can be under 0.5 cycle after smoothed, then the fast and accurate ambiguity resolution is realized.