The characteristics of AC/DC hybrid system faults are different from those of AC systems, which will affect the reaction of traditional AC protections. For the power frequency variation distance protection, firstly, the variation range of equivalent impedance angle of protection back system is analyzed from the perspective of quadrants, and then its action characteristics are further assessed. The results show that the protection range of power frequency variation distance protection in AC/DC hybrid system will be reduced, the anti?transition resistance capacity will be weakened, and the protection range may be completely lost in some extreme cases. To solve this, the reliability coefficient is diminished, the cosine value of phase difference of zero sequence current on both sides is used to avoid misoperation outside the area, and thus an improved measure of power frequency variation distance protection based on zero sequence current phase compensation can be proposed. An case study platform is built on PSCAD/EMTDC to verify the correctness of the theoretical analysis, and the effectiveness of the proposed improvement measures.