In this paper, composite silica gel and potassium formate as typical organic weak acid salts is proposed to use in desiccant coated heat exchanger (DCHE). An experimental study on dynamic adsorption performance of desiccant coated metal sheet samples is conducted to obtain results with different proportions of silica gel and potassium format. A DCHE testing platform is then used to compare thermodynamic performance between single silica gel coated heat exchanger (SCHE) and composite potassium formate and silica gel coated heat exchanger (PSCHE). It is found that impregnating potassium formate into porous silica gel is an effective method to improve adsorption capacity, and 75% saturated potassium formate solution is recommended to constitute composite desiccant under experimental conditions. Compared with SG coated sheet, on average the maximum adsorption mass of SG&0.75PF coated sheet increases 2–3 times. Besides, PSCHE can obtain about 20% higher moisture removal capacity compared with SCHE under experimental condition, meaning the utilization of composite silica gel and potassium formate desiccant can effectively improve dehumidification capacity. PSCHE also can obtain 50% higher total cooling capacity compared with SCHE. •Composite silica gel and potassium formate desiccant is proposed.•Experiments are conducted to obtain dynamic performance.•75% saturated potassium formate solution is recommended.•Composite desiccant and its coating heat exchanger have improved performance.