This thesis emphasizes on the harmonic currentflow in electrical power system using ClGRE's model oftransmission line and other electrical componentsexisted in the power systems. The procedure is firstlydone by forming admittance matrix (Y(,BUS)) at eachrequired harmonic frequency. Then calculate bus voltage(V(,BUS)) at that frequency by assuming harmonicsources as harmonic current sources. Developed software can analyze harmonic currentflow, both in harmonic current amplitude and directionof the flow by taking all conditions that will affectthe flow into account, e.g. impedance of power system,configuration of transformer winding, size and locationof capacitor bank and also location, size and tuningfrequency of harmonic filters. Furthermore, the software can evaluate totalharmonic voltage distortion (THD(,V)) at variousbusses. This leads to an assessment of harmonicperformance in electrical power system compared tointernational standards.