Abstract: The mechanism of the impact reshaping is studied. The formula of stress wave function at wave source is derived based on the impact dynamics and wave spread theory. The decay model of the stress wave spread is determined. The decay coefficients of the stress wave are determined by considering the well liquid, casing pipe and cement loop as a whole system. The stress distributions in the casing and cement loop are obtained. In order to validate the formulas proposed in this paper, the damage length of the cement loop is calculated according to the criterion of the cement material damage. The results agree well with those of tests.