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The so called "alterable-element method" (AEM) was introduced to deal with the coupling interaction of vehicle and sub-structure considering the actual transient jump of wheel, while the classical "contact all along" assumption based on which wheels and lower structure are always contact was abandoned. The alterable element used in this method is a conceptional element, which is used to calculate the coupling interaction of upper and lower structures and has some typical characteristics: firstly it flows along with the moving of contact point; secondly whether it is used for calculation depends on the contact state; thirdly its sizes could change according to specific problems and so on. VISUAL FORTRAN program was coded, and different moving vehicle models were presented taking into consideration the effects of random corrugation in the numerical study. The numerical solutions are favored comparing with the results obtained by alternative methods when there is no jump phenomenon existed. With abrupt irregularity, the transient jump of wheel was studied using the present method.Nomenclature Mv, Kv, Cv, uv-General mass, stiffness, damping and displacement vectors of vehicle Mwi-Mass of wheels lc-Half length of vehicle body lcc-Length between two adjoin wheels of two adjoin vehicles K1, C1, K2, C2-Stiffness and damping coefficients of primary and secondary suspension of vehicle Jc-Rolling moments of vehicle body and bogie Nw, N wtotal -Numbers of wheel on the bridge and total numbers of wheels Fi(i = 1, 4 × N wtotal )-Force acting on wheel KH-Equivalent contact stiffness coefficient xwi-Coordinate of the ith wheel u b (xwi, t)-Displacement of bridge pi-Contact force of the ith wheel and substructure F -Total force vector of vehicle-bridge system lwi(i = 2, 4)-Distance from the ith wheel to the first wheel of vehicle

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