Abstract: In order to guarantee the fly safety of certain helicopters main blade after prolonging life, the materials rupture performance test was carried on the fatigue danger parts of the helicopters root tie-in, and then the test data were analyzed and disposed. Through calculation, different crack growth lives among different crack growth formulas were contrasted. Then the crack growth lives were analyzed with the crack growth formula of full range Forman formula with reliabilities, and the inspection periods were given.