Distribution characteristics of zero-sequence current when parallel transmission lines grounding fault happens，the impact of zero-sequence mutual inductance on phase-earth distance protection，the setting method of zero-sequence compensation coefficient（K values）in grounding distance protection，and the impact of different K value setting schemes on protecting range of action are analyzed.With the simulation analysis of ultra-high voltage（UHV）1000kV Anhui-to-east power transfer parallel transmission lines，change trajectories of fault calculating impedance under different working conditions along the line，the setting reference values and protecting action range of zone I distance with different zero-sequence compensation coefficients are given.Finally，combining with the engineering practice，and considering the setting convenience and the protection sensitivity and safety，referential setting schemes for distance protection related constant values are proposed.