Abstract The objective of this thesis is to perform the AC/DC load flow and harmonic analysis for the power supply system of mass rapid transit (MRT) system. According to the computer simulation of stochastic harmonic load flow analysis, the mean value and standard deviation of voltage harmonic distortion are derived. The mitigation of harmonic distortion has been proposed by the proper design of harmonic filter. The mathematical model of 12 pulse uncontrolled rectifiers without interphase transformers is derived and applied in the AC/DC load flow analysis. The system voltage profiles and power consumption are obtained by computer simulation with the models derived. The Taipei MRT system is selected for simulation to solve the peak and off peak load of target year, bus voltage and power demand, and the harmonic current injection of traction substation. The voltage harmonic distortion is then calculated for each time snapshot according to the operation modes of all train sets on the main lines. According to the dynamic load behavior of train sets, the stochastic harmonic load flow analysis is executed to find the variation of harmonic distortion. To improve the power quality of MRT power systems, the proposed hybrid filter, which consists of both passive filter and active filter, is considered in the simulation. It is found that better distortion mitigation can be obtained with the hybrid filter by taking into account the stochastic harmonic current injection at the traction substations.