Abstarct: In the power system the frequency can be controlled by adjusting the generator outputs in response to load changes. At the present, due to high penetration of renewable energy and low efficiency of traditional generator in the microgrid, the load participation in the frequency control has received many attentions from technical and economic aspects. In the power system the balance between generation and load is important and the mismatch between generation and load leads to instability in power system. In this thesis, demand response and consumers potential are used in load- frequency control. Therefore, presenting a model for using the demand response in load frequency control is important. In this thesis, a model is developed by which the effect of load response in load frequency control is considered. This helps in adjusting balance between load and generation. To do this the power system equations in two cases with and without load response are extracted. Then, after solving these equations the effect of load response in the load frequency control are observed. In this thesis the optimal control is used to have better performance in the frequency control. The weighting matrices in the objective function are determined using the PSO, algorithm. The results of the simulation show that using the load response in the load frequency control leads to decrease in the frequency deviation.