Abstract: The integration of electric power system（EPS）and natural gas system（NGS） to construct integrated energy system（IES） is playing a key role in energy structure optimization in China, which can effectively lower the environmental pollution level and escalate the utilization efficiency of end-use energy. This paper takes NGS-EPS, a revised IES integrated from IEEE 14-bus test system and Belgian gas network, as the case. Aiming at minimizing the total running cost of NGS-EPS and the environment system,the paper establishes an optimized model through simplifying the computing method of non-piping elements and combining the pollutant discharge control method in environment management. NOx and SO2 are selected as environment control factors, and system security constraints and pollutant discharge concentration constraints are the chosen constraints of this model. It applies the interior point method to solve the OPF of gas-electric IES, compares and analyzes the effects of environment factors on IES, analyzes the environmental synergy of IES.