Provided are a polymer composition on a substrate and a surface modification method which is non-selective to substrate materials. Chemical vapor deposition polymerization is used to deposit a maleimide-functionalized poly-p-xylylene coating on a substrate. The substrate is readily available to perform a thiol-maleimide coupling reaction under mild conditions so as to modify the surface thereof. Furthermore, through a tailored thiol-terminal molecule, a designer surface can be created via thiol-maleimide coupling on a substrate, and the resulting surface can exhibit various desired biological functions for biotechnological applications. Therefore, this modification technique can be applied to biological fields extensively.