The present disclosure relates to a method for making a conjugated polymer. In the method, polyacrylonitrile, a solvent, and a catalyst are provided. The polyacrylonitrile is dissolved in the solvent to form a polyacrylonitrile solution. The catalyst is uniformly dispersed into the polyacrylonitrile solution. The polyacrylonitrile solution with the catalyst is heated to induce a cyclizing reaction of the polyacrylonitrile, thereby forming a conjugated polymer solution with the conjugated polymer dissolved therein.