Abstarct: Load modeling is a process of obtaining a mathematical equation for representing the behavior of the connected loads to a defined bus in a power system. In this thesis, developing above definition to a bus with high generation by DG units, we extract a mathematical model for static and dynamic behavior of distribution network from the viewpoint of the superior transmission network. Using these equations, all of the elements of inferior distribution network may compact to a composite load model. This model consists of a ZIP static load (constant impedance, constant current and constant power), parallel with an induction motor as a dynamic load. We used Particle Swarm Optimization for estimating the model parameters. As a new concept, the model of high generative distribution feeders with injected net power to superior transmission network is investigated. The necessary measuring data is obtained by a sample 20-bus distribution system simulated by ETAP software. This data is considered as an input data for parameter estimation in MATLAB software.