To study the effects of different levels of potassium(K) and boron(B) on cotton growth and B and K use efficiency,a pot experiment was conducted at Huazhong Agricultural University.The results showed that:compared with the normal treatment(K 20 mg/L， B 0.2 mg/L),low K treatment(K 2 mg/L,B 0.2 mg/L) inhibited the growth of shoot and dry matter accumulation，chlorophyll synthesis and B absorption of cotton,but the growth of root was promoted;lack of B treatment（K 20 mg/L,B 0.002 mg/L）dry matter accumulation of cotton and K absorption were lower;and the normal growth and dry matter accumulation and SPAD of cotton were decreased significantly when both short of K and B(K 2 mg/L,B 0.002 mg/L),the use efficiency of K was increased by 143%,and the use of B was restrained.The results showed that K deficiency decreased B absorption and utilization of cotton,and B deficiency inhibited K absorption and utilization of cotton,while both deficiency of K and B promoted the use of K and restrained the use of B.