The structural durability of wheel loader are required to estimate on the basis of design loading spectrum, which is a spectrum combination of various operating and loading conditions. To generate the load spectrum of transmission system, an actual operational loads of wheel loader under the driving cycle was investigated. A signal collection system was applied to get time-history voltage signals and then torque loads were obtained according to the conversion coefficient between voltage and torque. After zeroing and filtering, the mean, the amplitude and number of load cycles were gained with the rain-flow counting method. The mean and amplitude were tested by Nominal distribution and Weibull distribution respectively. Test results show that they are independent. The two-dimensional joint probability density function of amplitude and mean was gained. After extrapolation, the load spectrum of the spacerflange under whole-life cycle is gained and the process of compiling load spectrum is also provided.