In order to study the composite load modeling of distribution network with microturbine（MT）， the MT system is established and the models of each function module and control strategy are expounded. Through the analysis of the dynamic performance of a MT power generation system in transient， the MT could be considered as a generalized dynamic load which consumes negative power. Based on this， the first-order differential state equation is proposed to describe the dynamic characteristics of the MT system. This description model is based on rotor angular velocity of permanent magnet synchronous generator（PMSG） as state variable. The validity of this equivalent description model is validated by comparison of simulations with different disturbance levels.