According to internal heat and moisture transfer coupling equations for the humidity-controlled composite materials in greenhouse, the analytical solutions are obtained under the steady periodic conditions, then the moisture desorption and adsorption properties of humidity-controlled composite materials in a closed space are investigated. It shows that the air humidity ratio in the closed space changes periodically in consistent with the air temperature. The ratio of the absolute humidity amplitude to the air temperature amplitude is a constant, which can be taken as a criterion to evaluate the humidity control performance of the material. A simple method, the close box and heat impulse method is put forward to measure the constant value. It can directly embody humidity-controlled traits of materials under the condition of periodic heat and moisture.