Abstract: Considering that the present composite mechanism load models have imperfections in model structures,a PI-type composite mechanism load model was proposed and was established.In the model,the high-voltage distribution network is equivalent to an impedance,in series with an ideal transformer which was approximated with a PI-type circuit.According to inverse voltage regulation principle,the voltage ratio of the ideal transformer was determined with the average voltage of the high-voltage bus in the steady state,which can reflect the result of the distribution network voltage regulation.Static load was described by using ZIP model,the effect of reactive power compensation considered.This model can better concur with the general structure of the distribution network and has no additional parameters.Case study shows that the composite load model proposed in this paper has better performances than the present composite load models in self-describing and generalization abilities,and has some significant advantages in reflecting the voltage regulation ability of the power grid,maintaining the load bus voltage stability and the fitting performance to dynamic behavior of the load at different voltage.