Abstract: The waste walnut shell was used to prepare biomass porous carbon (PC). Capric acid (CA) was encapsulated into the PC by vacuum absorption. And the CA-PC composites were prepared. The CA-PC/Di-Gy multi-functional composites were made by CA-PC composites, diatomite (Di) and gypsum (Gy). The thermal property, heat property and moisture property of the CA-PC/Di-Gy multi-functional composites were tested respectively. The prepared samples were characterized by using BET, FTIR, SEM and DSC. The results show that the PC made by waste walnut shell has high developed pore structure which not only can package CA but also can adsorb formaldehyde. The temperature-humidity control property and adsorption rate to formaldehyde of the CA-PC/Di-Gy multi-functional composites are good. The constant temperature platform is about 32℃. The equilibrium moisture content is 0.0859-0.2310 g/g during the 40%-60% reality humidity. And the adsorption effect is close to 40% after 4 h of formaldehyde.