Aiming at the relative position requirements of collaborative awareness and signal-level task collaboration in swarm of UAV, the paper first analyzes and establishes the double-difference model of Beidou carrier phase differencing positioning, focusing on the processing flow of moving coordinate carrier phase difference positioning and the compensation method of age error. Then set up the test platform in the vehicle and launch the experiments in the running. The test results show that the accuracy of the carrier phase differencing positioning reaches centimeter-level, which meets the signal-level relative position requirements in swarm of UAV.