An E.coli-expression mutant library containing 1 000 cry mutant genes was constructed using DNA family shuffling method with five initial cry genes cry1Ac,cry1Ab,cry1C*,cry2A* and cry9C*.The 1 000 clones were expressed in E.coli and their toxicity was tested upon Helicoverpa armigera (cotton bollworm) larvae.The expression level of mutation clones were quantified by ELISA.Compared with the original Cry1Ac,there were 122 clones with significantly enhanced toxicity,38 clones with similar toxicity; 232 clones with decreased toxicity; and 608 clones with lost toxicity.All 1 000 cry mutant genes in the library were sequenced and amino acid sequence homology of all cry mutant genes was analyzed by multiple comparisons.Gene sources of 945 clones were found and divided into 5 classes based on homology,55 clones were unrecognized.According to toxicity level,the 1 000 clones were further divided into 3 classes:increased toxicity,similar toxicity and decreased toxicity.Analyzing the amino acid sequences of the 1 000 clones,the homology in 5 decreased toxicity classes was lower than increased toxicity classes and similar toxicity classes.