Corn stover fibers were modified by 4% silane coupling agent. Then the contact angles of three different wetting liquids against unmodified and modified corn stover fibers were measured by capillary rise method, based on Washburn equation and the method of Owens-wendt-Kaelble, the surface tension and its components of unmodified and modified corn stover fibers were calculated. The results showed that the surface tension (31.2 mN/m) of high-density-polyethylene (HDPE) is lower than that (22.20 mN/m) of modified corn stover fibers, so HDPE could spread out on the surface of modified corn stover fibers more easily. Moreover, the polar component of surface tension of modified corn stover fibers decreased from 22.20 mN/m (unmodified) to 3.51 mN/m, therefore, modified corn stover fibers have better interfacial compatibility with thermoplastics.