Good magnetic properties of Ce17Fe76.5B6Nb0.5Cu0.5Ga0.5 alloy were obtained in our previous study. In order to increase the Curie temperature of Ce-Fe-B alloy without reducing the magnetic performance, Co element was added to optimize the composition of Ce-Fe-B based alloy. The effect of Nb, Cu, Ga, Co co-addition on phase structures, magnetic characteristics, microstructure and Ce valence state weight of Ce-Fe-B alloy are discussed comprehensively. Magnetic properties of Jr = 0.43 T, Hci = 486 kA/m, (BH)max = 30 kJ/m3 and TC = 437.8 K were obtained in Ce17Fe74.5B6Nb0.5Cu0.5Ga0.5Co2.0 alloy. An obvious remanent magnetization enhancement, decreased recoil permeability and fully closed recoil loops are observed for the optimized alloys. The strengthened short range exchange coupling interaction between adjacent grains contributes to the increased remanence ratio. The synchrotron radiation X-ray absorption near-edge structure fitting result showed that the magnetic Ce3+ valence weight of optimized alloy increased, while the nonmagnetic Ce4+ valence weight decreased compared with the original alloy. Microstructure observations showed that the triple junctions of tetragonal main phase grains are rich in Cu, while Co element prefers to enter into CeFe2 phase. The improved magnetic properties are mainly due to the increased Ce3+ valence weight and strengthened intergranular exchange coupling interactions.