In this paper, a novel power generation system integrating a natural gas expansion plant with a geothermal organic Rankine cycle (ORC) was proposed. The paper begins with an introduction to the thermodynamic and economic models of the system. Secondly, contrastive analyses of three candidate working fluids were made, leading to the selection of R600 as the best fluid for the system, and the effects of gas pipeline parameters fluctuation on the system performance were originally investigated and analyzed based on the actual operating data of a natural gas PRS, located in Xiqing district, Tianjin, China. Finally, a multi-objective optimization for the system using R600 as working fluid was done to find the optimal evaporation temperature based on the TOPSIS decision-making method, and exergy loss analysis was accomplished at the optimal condition. The results indicated that the proposed system had a net profit of 3.97 M$ in the life time and a small payback period around 2.0 years at the optimal evaporation temperature of 45.5 degrees C where the system had a high thermal efficiency of 89.8% and exergy efficiency of 84.13%. Additionally, the condenser has the greatest potential to reduce the total exergy loss of the system. (C) 2018 Elsevier Ltd. All rights reserved.