Our study focuses on environmental risk assessment of a gas power plant in southern Iran. In this research, after investigating the different activities and processes of the power plant, potential harmful factors were initially identified. Afterwards, the identified risk factors were assessed and classified regarding the severity and probability of occurrence, possibility of recycling, and dispersion of pollution into the environment. The EFMEA method was applied to assess the risks. In order to improve the EFMEA technique, the integrated EFMEA and TOPSIS method was used. The method was suggested to remove the uncertainty arising from EFMEA and perform a consistent and logical analysis. Accordingly, using TOPSIS, the weights of the risks were multiplied to a risk priority number (RPN) of environmental aspects. The results obtained from comparing the calculated risk numbers showed that the risk of explosion and gas leakage caused by commissioning the unit with gas-fuel (with RPN equal to 163.014) assigns itself the first priority amongst other risks. The proposed technique has high potential impact on managerial policy within environmental decisions. Considering the application of expert opinion, the suggested TOP-EFMEA method is more flexible than EFMEA.