The effect of chemical treatment with HCl solution on the wetting properties, surface morphology, thermal properties, fineness and mechanical properties, chemical structure and microscopic state of aggregation structure was investigated for polyimide fiber-reinforcements The results show that after HCl treatment, the fiber surface exhibits characters of etching with increased surface roughness, higher surface free energy, and enhanced wetability, while certain reactive group is introduced onto the surface; With the increase of HCl concentration, the rise of temperature as well as the the increase of processing time, the wetability was sharply enhanced, the fineness and mechanical properties decrease slightly while the thermal property keeps preferably within a certain range. The existence of H⁺ in the treatment solution could result in that a few of imide rings on the fiber was broken and then hydrolyzed to polyamide acid, thereby its microscopic state of aggregation structure was changed and the ratio of amorphous region was enhanced, therewith its chemical structure does not change significantly. In general, HCl treatment is feasible for modifying the polyimide fiber surface.