Abstract: In view of the quality problems such as insufficient surface hardness, uneven and discontinuous nitrided layer thickness in C60 steel strip during gas nitriding treatment, the microstructure evolution law, nitrided layer morphology and influence factors of properties were studied systematically. By comparing the microstructure of annealed-rolled state and tempered state before nitriding, it is found that tempering at 580 ℃ can promote uniform carbide precipitation and internal stress relief, reducing the matrix hardness from 200 HV to 160 HV, which facilitates nitrogen diffusion. The results show that the surface hardness of the qualified nitrided products exceeds 550 HV, while that of nonqualified ones is below 450 HV, and the nitriding layer thickness is below 5 μm. The SEM observation shows that there is no continuous and dense nitride layer on the surface, and even "exposed matrix" appears locally. The EDS analysis show that the unqualified area is enriched with O element, which is speculated to be caused by the failure to remove the oxide film, which hinders the adsorption of nitrogen atoms. An improved process was proposed: extending tempering time to 4 h, adding acid pickling and ultrasonic cleaning prior to nitriding, and optimizing ammonia dissociation rate and furnace temperature uniformity. After optimization, the nitrided layer thickness increases to an average of 12 μm, the surface hardness reaches（570±20） HV, and the product pass rate improves from 65% to 92%. The study provides theoretical support and technical guidance for nitriding process optimization of high carbon steel strips.