Abstract: In order to explore the effect of boll setting period on fiber quality of early cotton in Southern Shanxi, and provide theoretical support and important basis for breeding early-maturing varieties with high fiber quality,‘CCRI 50’and‘Jinmian 57’were taken as materials to analyze the influence of the boll setting period length on fiber quality. The results showed that the fiber quality of‘CCRI 50’was the best when the boll age was 73-days, the fiber length was 29.01 mm, the uniformity index was 84.60%, and the fiber strength was 28.7 cN/Tex. On the other hand, the fiber quality of‘Jinmian 57’was the best when the boll age was 79- days, the fiber length was 28.75 mm, the uniformity index was 84.40%, and the fiber strength was 28.8 cN/Tex, and the fiber strength of 79-days was 0.1 cN/Tex lower than that of 73-days. In general, the fiber length, uniformity, strength and micronaire of early cotton fell down with the shortening of boll setting period, while the elongation showed a rising trend with the shortening of boll setting period. Among the 5 indicators, the influences of boll setting period on fiber strength and micronaire were the largest.