Abstarct: Recently due to lack of nonrenewable sources, the human being tries to use renewable power such as sun power, wind power and etc. The renewable system can be grid connected or grid disconnected (islanded mode operation). One of the most important issues in these systems in small signal stability analysis. In this thesis the small signal stability of renewable systems has been investigated in the islanded mode operation. In order to study the microgrid behavior baxsed on differential equations in the state space, the small signal model small part of the network are written in the space state. Then by combination of this equation, the final model for study the system has been obtained. To investigate the sensitivity of the eigenvalues of the system with respect to the system parameters, the sensitivity analysis with respect to the droop coefficient has been performed. The eigenvalue analysis baxsed on the state space model has been carried out to find the changes in eigenvalues and also to investigate the small signal stability. Finally, the simulation of the obtained model has been undertaken in the Matlab software using. Also in the time domain simulation to compare the results of simulation to evaluate the effect of controller parameters and other parameters of the microgrid system on small signal stability, as well as the impact of constant power load that has been loaded on small signal stability.