Research conclusions:From the research it is concluded：(1)Loading the prestress Call decrease the vertical stress by about 0．2 MPa，and in the meantime，it also can strengthen the rigidity of the structure，and its dynamical amplification coefficient is bigger than that of normal structure，but the amplification is not big．(2)Loading prestress or unloading prestress has no obvious influence on the calculation results because there is no joint vibration due to the big difference between the self—frequency of the structure without crack and the air dynamic load frequency of train．(3)There is no big difference between the top displacement of the structure under the air dynamic effect of train and the top displacement of the structure under static effect．(4)The structure is in elastic working stage under the air dynamic effect of train．