Abstract: In order to clarify ripening effect of Pyraflufen on cotton, and further define the influence of the ripening effect on yield and quality, we analyzed the leaf shedding speed, boll opening rate, yield, etc of cotton using the field experiment and laboratory efficacy test. Results showed that 2% pyraflufen ME could promote defoliation and boll opening obviously, which was similar to thidiazuron. The yield of seed cotton was 10.75% to 21.60% higher than that of water control area after treated 30 days. The amount of blossom before frost significantly increased, meanwhile weight of single boll decreased and stiff boll increased. The pesticide had no obvious effect on lint, fiber length and other qualities. Pyraflufen should be applied as a new type of defoliant and ripening agent with many advantages, such as good security, rapid defoliation, boll early-opening and high proportion of pre-frost blossom.