The present invention relates to a method of synthesizing a bigraft compolymer based on grafted type peracid polymer, which comprises graft polymerizing a first ethylenically unsaturated monomer containing a carboxyl group onto a polymer substrate having a form of a membrane, particulate or tube; oxidizing the carboxyl groups of the resulting graft polymer into peracids; and then graft polymerizing a second ethylenically unsaturated monomer onto the grafted chain of the graft polymer through the decomposition of the peracid. Surface profile and morphology of the bigraft copolymer membrane product is also investigated by scanning electron microscopy and transmission electron microscopy respectively.