Abstract: To understand the hygroscopic coefficient different on the bamboo and poplar, the hygroscopic coefficient of Moso bamboo strip and poplar veneer in different humidity process were tested by the resistant strain sheet. The results showed that the hygroscopic expansion coefficients of poplar in longitudinal and transverse dimension are more than 2 times those of bamboo in the period of dehumidifying. Bamboo displayed an obvious lag response to environmental temperature and relative humidity change compared with poplar veneer. The warp of poplarbamboo laminated in longitudinal dimension mainly depended on poplar’s deformation. During the dehumidity process, the warp will be made from bamboo surface to the poplar back, and high humidity treatment will make the warp from poplar back to bamboo surface under the difference between hygroscopic expansion coefficient and lag response to humidity.