Laser Raman spectroscopy was employed to characterize the microstructure variations of polyacrylonitrile-based carbon fibers during electrochemical treatment, and the characteristics of first-order Raman spectra of carbon fibers with different treatment time were investigated in the present paper. The results indicate that the Raman spectra of the carbon fibers can be fitted into four bands,named as D (or D1) band,G band,D2 band and D3 band, respectively. The Raman parameters to characterize surface microstructure variations of carbon fibers mainly include R(ID/IG,area ratio of D band and G band),ID２/IG(area ratio of D2 band and G band),ID3/IG(area ratio of D3 band and G band),and IDS/IG(area ratio of all the disordered structure and G band). The peak separation between D band and G band becomes large after electrochemical treatment. R increases,which indicates that the surface disordered degree of carbon fibers increases. ID3/IG increases,which is caused by organic molecules,fragments or functional groups; decreases which is caused by the break of the aliphatic structures. With increasing treatment time,IDS/IG increases continuously,and the change trend of IDS/IG is consistent with that of R value,which can be used to comprehensively explain the variation of the surface structure of carbon fibers. So,the variety rules of the structure of carbon fibers can be investigated by laser Raman spectroscopy during electrochemical treatment.