Indirect evaporative cooling (IEC) and liquid dehumidification (LD) have a great energy-saving potential in air conditioning. This article presented a novel heat and mass exchanger integrating the IEC and LD (IECL), which can save the space of the air conditioning system and stably use the latent heat generated by the primary air condensation to improve the heat transfer rate. To investigate the performance of the IECL, a model was established to simulate the heat and mass transfer processes and validated by the experimental data. The pressure loss, total energy consumption, and COP were obtained under different heat exchanger structural parameters. Additionally, the moisture content and temperature difference between the primary air inlet and outlet, dehumidification efficiency, wet-bulb efficiency, and cooling capacity of the optimized IECL were investigated under different operating conditions. The results indicated that the optimized channel gap and length should be set as 5 mm and 600 mm, respectively, and the peak value of the COP is 173.3. Moreover, the IECL showed a good cooling capacity in hot and humid areas. Under the simulated conditions, the dehumidification efficiency ranges from 50% to 77%, and the wet-bulb efficiency ranges from 21% to 60%.