To study the function of the all3555,an over-expression strain and a deleted mutant strain of all3555 in Anabaena PCC 7120 was constructed.The defected mutant strain was found to grow in usual condition but be more sensitive to NaCl under salt-stress.When all3555 was over-expressed,the resistance of Anabaena PCC 7120 to oxidative stress and NaCl under salt-stress was improved.Results showed that all3555 almost didn’t affect the growth of Anabaena PCC 7120 under the normal condition,but it was important for the resistance of Anabaena PCC 7120 to oxidative stress and NaCl under the salt-stress.