The isolated neutral distribution power system in China is permitted to continue operating for two hours after single-phase earth fault. This paper researched the influence about distribution network electricity metering loop technically in such case to make up the lack of attention before. This paper inferred the mathematical physical model of electricity metering loop and expressions of line loss under single-phase earth fault. Models and expressions were verified by simulation. It is concluded that electric energy metering loop on the load side is effected by the single phase earth fault while the one on power supply side is not effected.