Abstract Internally-cooled membrane-based liquid desiccant dehumidifier (IMLDD) can well alleviate the dehumidification deterioration due to the increase of desiccant solution temperature. In the IMLDD, air channels and desiccant solution channels are separated on both sides of semi-permeable membrane. Cooling media flows through tubes inside solution channels to reduce desiccant solution temperature. There exist many flow patterns of fluids (air, desiccant solution and cooling water), which have been proved to have significant effects on the performance of IMLDD. Therefore, to find the optimal flow type of IMLDD and operating conditions, the mathematical model for IMLDD was developed and validated experimentally, and the exergy and entransy theories were first adopted to analyze the effects of inlet parameters on the performance of IMLDD of various flow types. The results showed that counter flow arrangement between air and solution and parallel flow arrangement between solution and cooling water had the best dehumidification performance. The trend of dehumidification efficiency was opposite to exergy efficiency with the increase of inlet air humidity ratio and solution concentration. The increase of inlet cooling water temperature improved exergy efficiency but decreased dehumidification efficiency accordingly. The research of this paper is helpful for the design and optimization of IMLDD.