Low-temperature heat source has been exploited for decades to generate electricity. Organic Rankine cycle (ORC) system has a high energy conversion efficiency due to the good performance of organic fluids under the low-temperature heat source. In this study, a double-pressure organic Rankine cycle system driven by low-temperature heat source is used to generate electricity. The double-pressure ORC system achieves the cascaded utilization of energy, which can improve the efficiency of energy conversion. Geothermal heat source is employed as a typical low-temperature heat source. Mathematical model is established based on thermodynamic and economic laws, and the overall system performance has been evaluated. Parametric analysis is conducted to examine the effects of some key thermodynamic parameters, namely turbine high-level inlet pressure, turbine low-level inlet pressure, turbine high-level inlet temperature, on the system's performance. Multi-objective Parametric optimization based on turbine 1-D design is conducted by means of genetic algorithm (GA) to find the best operation conditions for both economic and thermodynamics. At the same time, the performances of three organic working fluids are examined. Results indicate that the double-pressure ORC system has a better performance than single-pressure ORC system, and R245fa has a better performance among three organic fluids. It is also found that the exergy efficiency has a peak value with the change of turbine high-level inlet pressure and turbine low-level inlet pressure. In addition, increasing turbine high-level inlet temperature brings a positive effect on the system performance. Exergy analysis is also conducted and the result indicated that the main exergy loss occurs in high-pressure evaporator. After system optimization, the double-pressure organic Rankine cycle has a better performance in utilizing geothermal energy than single-pressure system. (C) 2018 Elsevier Ltd. All rights reserved.