According to the electrical parameters of subway train of Zhengzhou metro transit line 1,this paper estimates the maximum traction power which is acquired from the traction networks when the subway train is towed with four kinds of load conditions.Then mathematical models of traction load are built on the basis of the results.Taking advantage of Simulink tool in MATLAB, the AC simulation models of the metro power system are built when the train is towed in early, short,long term and typical kinds of load conditions and the AC-DC power flow calculations are completed through the interactive operation with computer programs.Besides,this paper builds an equivalent model of 24-pulse rectifier and makes up compute programs to calculate the harmonic power flow by forming the harmonic equivalent circuit with each harmonic mathematical model. Finally,the harmonic characteristics of Zhengzhou Metro and the influences of harmonics on urban distribution network can be achieved according to the calculation results of harmonic power flow and we can take some effective measures to reduce the influence of harmonics.