The rice husk powder was modified by polymer (lactic acid) (PLA) and Maleic anhydride (coupling agent, MAPP). Composite material was prepared in the way of melt blending. The mechanical properties, water absorbability of rice husk/polymer (lactic acid) (PLA) composites, and the relations between these properties and microscopic characteristics were investigated. The result showed that, with the increasing content of rice husk power, the maximum bearable tension and tensile strength increased; Water absorbability after 2 hours’ immersion hadn't significant change, but after 24 hours’ immersion, the water absorbing capacity had obvious addition. The study also showed that coupling agent could significantly reduce the water absorbability of composite materials; The use of scanning electron microscope (SEM) found that the interface became smoother, the adhesion between PLA and rice husk powder became closer when add the coupling agent to the rice husk powder, it also could well explain the differences between water absorbability and mechanical properties.