Abstract: The compatibility of polyacrylonitrile /soybean protein blend(PAN/SPI) was studied with polarized microscope,FTIR,scanning electron microscopy(SEM) with focuses on the factors affecting the compatibility of the two components and the mechanism of hydroethyl methacrylate(HEMA) in improving the compatibility of this system.The results showed that this system of PAN/SPI has partial compatibility and their compatibility can be improved by adding hydroxyethyl methocrylate because hydrogen bond has been formed in soybean protein solution after treatemt.