The GNSS carrier phase measurements are more precise than pseudorange measurements while they would suffer cycle slip or losing lock because of the signal shielding or the other reason. For ensuring the accuracy and integrity performance of relative positioning based on carrier phase, the monitor of the integrity for the carrier phase should be introduced. The conventional method executes the carrier phase monitoring in observation domain that subject to the quality of pseudorange which would have poor effect. The article proposes the monitoring method based on position domain which achieves the phase carrier monitoring through the consistency check of the carrier phase residual. Simulation results show that the method could monitor the fault of carrier phase effectively which guarantees the accuracy and integrity of relative positioning.