Abstarct: Data envelopment analysis is a non-parametric method for evaluating the efficiency of decision-making units, which, baxsed on mathematical programming, recognizes the relative performance of envelopment analysis models is to identify and improve inefficient units. One of the situations in which the unit under evaluation is ineffective is when congestion occurs. When increasing one or more inputs decreases one or more outputs, or vice versa, decreasing one or more inputs increases one or more outputs so that other inputs and outputs remain unchanged, congestion occurs. This event is one of basic concepts in economics that neglecting it will damage the body of economy. Data envelopment analysis is a tool for invesitigating and identifying the event. In this thesis, we seek to evaluate the performance of 15 selected power plants in the country in terms of congestion. After reviewing the data envelopment analysis, the definition of congestion, congestion measurement models, finally, the selected of the Iranian electricity industry and the calculation of congestion through data envelopment analysis in this industry. According to the results, the highest congestion belongs to Hormozgan Power Plant and Yazd has the lowest congestion with 9% and also the highest congestion in Khuzestan with 78%. In contrast, Yazd had the lowest congestion rate of 17 percent. An overview of the results of the table shows that out of the 15 electricity industry, only one is relatively efficient.