In this work mathematical models of Steam Rankine Cycle (SRC) and Organic Rankine Cycle (ORC) power systems have been developed to explore the feasibility that combines the fluid-flow temperature, waste heat steam and low-boiling-point organic working fluids for power generation. The effects of the thermodynamic parameters on the SRC and ORC performance are examined. Among the commonly available working fluids, a selection based on environmental and technical criteria was carried out resulting in a list of 8 working fluids: R143a, R245fa, R600a, R124, R134a, RC318, R236fa, and Ammonia. Using the numerical models, we calculate and compare thermal efficiency, generating capacity, etc. of two power systems, namely SRC and ORC under the same heat source conditions. The results show that under the same condition of heat source, ORC has the highest thermal efficiency and power generation.