Abstract: The effect of potassium fertilizer application amount, fertilization method and different Bt cotton varieties were researched. The experiment was carried out on the farm of Anhui agricultural university and Suzhou city agricultural science institute from 2002 to 2003. The results were shown as follows: Compared with CK, contrast Transgenic Bt cotton which K fertilizer was applied in the same conditions, 2.3%~18.9% lint yield was increased and fiber quality was improved. K fertilizer applied amount for best profit was 375kg/hm2. The reason of production increase was that fruit branches, bolls, boll weight and lint increased and bolls ratio of quality increased obviously. The effect of 60% based dressing and 40% early flower period of K fertilization was the best. The experiment also declared that the effect was different between 32B and CCRI29. While in the same condition of K fertilization application, CCRI29 increased 12.7% in comparing with CK, 32B increased 11.2% in comparing with CK. 32B is sensitive to the potassium fertilizer obviously. CCRI29 increased 6.7% in comparing with 32B. Main physiological reason is that CCRI29 per plant increased more dry matter accumulation weight, especially from early flower to open stage. The dry matter accumulation weight of CCRI29 increased rapidly. The result indicated that hybridizing anti-sect cotton had remarkable hybrid advantage.