According to an HVDC system power modulation abnormal case, this paper analyzes the power abnormal modulation reason that the rectifier station receives the abnormal current reference from the other station based on the related events and recorded waveform before and after fault recovery. From the detailed analysis of the relationship among the total power reference, the total current reference, the DC current reference, the measured DC current value, and the role of the pole control DUST between the two stations, the inference which causing the abnormal current reference is the abnormal communication channel of the pole control between the two stations. The simulation projects are designed and reappeared in the simulation platform built in the laboratory according to the actual structure of the inter-station communication configuration. At last, it summarizes the related links which cause abnormal power modulation and gives corresponding treatments, which has guiding significance for similar power modulation fast processing in the HVDC system.