Organic Rankine cycle (ORC) power generation system is an attractive unit applied widely to exploit low-to medium-grade energy sources. This work proposes a thermodynamic analysis and optimization of a flash-binary geothermal cycle for power generation and hydrogen production aims where the binary cycle used is an organic Rankine cycle in which different mixtures of zeotropic fluids are used as the working fluid. The integration of ORC and zeotropic mixtures presents the considerable capability to combine their superiority and further enhance the system performance considerably. The superiority of the proposed system which combines the advantages of zeotropic mixtures with ORC positive aspects, is revealed through the energy and exergy analysis. Also, the particle swarm optimizer is employed to optimize the net output power as the objective function. The results reveal some precious facts; for instance, the overall thermal and exergy efficiencies are obtained 18.9% and 57.39%, respectively for the base case. However, the optimized results demonstrate that the Pentane (0.31)/Butene (0.69) and Pentane (0.41)/Butane (0.59) combinations hold the maximum energetic efficiency of 18.96% and 18.91%, respectively. The net output powers for these combinations are 125.712 kW and 124.923 kW, respectively. Besides, The highest exergy efficiency belongs to Pentane (0.31)/Butene (0.69) and Pentane (0.41)/Butane (0.59) combination whose values are 57.24 % and 57.10 %, respectively. Also, from the parametric study, it can be inferred that increasing the generator's pinch point temperature results in a lower power generation rate of the ORC and total system. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.