In order to study the composite load modeling of distribution network with microturbine generation (MTG) system, the grid-connected MTG system was established. The third-order differential equation of state description equivalent model of MTG system was presented, and the validity of this equivalent description model was verified. Based on these, the model structure of the generalized load model of distribution network with MTG system could be described as traditional synthesis load model paralleled with MTG equivalent description model. The model validation was testified by the simulation modeling of different disturbance levels and different load levels， The verification has indicated that the generalized synthesis load model proposed has good description ability, generalization ability and parametric stability.