Aiming at the problem that the Beidou satellite positioning system (BDS) has cycle slip in the carrier phase observation, the method of improved polynomial fitting model can make cycle slip detection and repair in carrier phase observation. This method uses the carrier phase observations with the same satellite measured by three receivers, combined the carrier with the phase between the receiver and satellite can measure two groups of single difference. Using a set of single difference with polynomial fitting can obtain the epoch number of cycle slip, using another group of single difference with polynomial fitting can determine which group to have carrier phase cycle slip, at the end of the week, repair the cycle slip. The experimental results show that this method not only can measure more than 0.2 jumps, but also can measure more than 0.2 week jump which group of carrier observations occurred.