Theories of transfer function are use to describe how to calculate random response of vehicle skeleton under road spectrum in this paper. First passage fail model combing with the basic theory of structural reliability, the calculation formula of dynamic strength reliability for vehicle skeleton is presented. Strength reliability for a bus body skeleton is solved by 13936 samples of Monte-Carlo Method when the bus is running on the C level road at a velocity of 80 km/h. The results of the numerical example show that the dynamic strength failure probability for the bus body skeleton is 8.90524×10-4 and corresponding reliability is 99.9991095%.