In the ±500 kV Baoji-Deyang HVDC project, Pole I and Pole II will put into operation in different stages. During the commissioning test of Pole II, the safe and stabe operation of Pole I is guaranteed by the isolation between two pole. In this paper, the interaction between two pole is analyzed in detail, factors are given and summarized. The isolation measures on both software and hardware are proposed, which can be further referenced by similar subsequent projects.