The energy consumption of HVAC&R systems is increasing rapidly and application of hybrid source systems is an alternative solution. Utilizing three-fluid heat exchanger in hybrid source HVAC&R system can make the system more compact in construction, higher in thermal efficiency and lower in reliability risk. In this paper, a simulation model of a fin-tube three-fluid heat exchanger is built with distributed-parameter method and validated by experimental data. Based on the demand of a new type of hybrid source system, the optimal circuit arrangement type and tube diameter are achieved. The heat transfer rates of the three fluids under different working conditions are investigated. The results also show that to ensure that cold fluid 1 is superheated in the outlet for the stable running of the system, flow rate and inlet pressure of the hot fluid and air inlet temperature should be higher than certain values, while flow rate and inlet pressure of cold fluid 1 should be lower than certain values. Air flow rate can be adjusted freely without range limit. This paper will help the design of fin-tube three-fluid heat exchanger and promote its application in HVAC&R systems.