Abstract: BDS regional system has been officially announced to provide positioning services over the Asia-pacific region at present. We investigate the performance of ambiguity resolution with combined GPS/BDS observations under this condition. Using observation data of the different-length short baselines and PANDA software analyze the success rate of ambiguity-fixing of GPS single system, BDS single system and GPS/BDS combined system, we find that the ambiguity of GPS/BDS combined system relative to each single system can be quickly fixed even if with L1 observation. Combine the theory of ambiguity resolution to analyze experimental results, and interpret the experimental conclusions in theory. The impact of system bias on ambiguity resolution of GPS/BDS combined system has been discussed. According to the experiment, we find the difference among fractional parts of the between-receiver SD-ambiguities is very small in the each single system, but the fractional parts of DD-ambiguities between GPS and BDS are big, however, which are stable. This provide a possibility to form DD-ambiguities by mixing SD-ambiguities of GPS and BDS by calibrating the system bias, which is highly beneficial for positioning under severe environment.