A circuit model of 10 kV reactive power compensation circuit of substation containing harmonic sources is established to study influence of three factors of ratings of harmonic sources on transition process of closing of power capacitor circuit.The model is established and simulated by the use of ATP-EMTP electromagnetic transit simulation software and by actual ratings to obtain a series of simulation oscillogram of overvoltage and overcurrent and make comparison of overvoltage and overcurrent of transition procedure of closing operation at different harmonic ratings.It is shown through theoretical analysis and simulation that harmonic ratings have big influence on overvoltage and overcurrent of transition procedure and the specific influence extent is depended on ratings of circuit and harmonic.