Wood flour/polylactic acid composites prepared by melt extrusion method with the glycerol were adopted as plasticizer to improve the compatibility between wood flour and polylactic acid. The effects of glycerol addition on the properties（compatibility, thermal stability, rheology, water absorption and mechanical properties） of composite materials were studied. The results of XRD and SEM show that the best compatibility between wood flour and PLA is obtained when the glycerol addition is 9%（mass fraction of wood flour/PLA composite materials）. To get smaller water absorption, 6% glycerol addition is appropriate and the water resistance is the best. With the addition of glycerol, the tensile strength and bending strength first increase and then decrease, and reach a maximum value at 6% glycerol addition.