Through theoretical analysis, the thermal performance of direct-contact air-conditioning system was studied. The analysis overcomes some shortcomings of the analysis in 1996 ASHRAE Systems and Equipment Handbook and 1997 ASHRAE Fundamentals Handbook. The influence of various factors on the characteristics of heat and transfer of such systems was analyzed. A general formula for the heat exchange efficiency of parallel or counter flow direct-contact air-conditioning system was obtained through theoretical analysis, which is with the same type of empirical relations. The heat exchange efficiencies of the processes of cooling and dehumidifying of air by using parallel-flow and counter-flow systems were calculated. Those data agree well with the experimental results in the literature. The analysis method together with some results presented in this paper is helpful to the design, adjusting and simulation of the thermal performance of such systems.