Compared with traditional deterministic structural static analysis, it is more practical that strength reliability analyses for bus body frames involving uncertainties in material and in geometrical parameters. In this paper, basic theories of structural reliability combined with bus driving characteristics, the concept of strength reliability for bus body frames and calculation method based Monte Carlo method are proposed. The formula of sensitivity of performance function to random variables is derived. Strength reliability figured for a bus body frame is 0.999626851 in the case of running with uniform velocity. Main random variables which effect on strength reliability are found via sensitivity analysis. All of works done can be applied to bus body frame designs based reliability.