Abstract To solve the problem of low thermal efficiency and single output form of the basic organic Rankine cycle, a parallel type organic Rankine cycle and ejector heat pump combined cycle is proposed. By deeply utilizing the energy of the low and medium temperature heat source, the system can provide different proportions of power and heating water according to users’ demands. Considering the factors of performance, environmental impacts, flammability, and turning point temperature, five working fluids are selected (i.e., R236ea, R123, R245fa, R365mfc, and R141b). Parametric analysis of the system is performed by constructing the thermodynamic model. Different operating modes of the system are defined according to different heating/power ratios. The results show that each working fluid has its optimal generator temperature to optimize the net power output efficiency. R236ea is more suitable for the system with a net power output efficiency of 6.58% and an exergy efficiency of 42.24%. Compared with the series type combined cycle, the parallel type combined cycle net power output increased by 5.08% and heating capacity increased by 20.71%. This paper can guide the efficient construction of low and medium temperature cogeneration systems.