In order to solve the problem of load expression of transmission test bench under non-stationary random cyclic load conditions, a parameterized test load model for typical shifting condition reconstruction was proposed. Taking the transmission drive shaft of the typical shifting condition of loader as research object, the non-stationary random load data was decomposed into non-stationary deterministic component (trend term) and stationary random component (random term) based on the wavelet transform series decomposition method. The trend items with non-stationary random characteristics were parameterized by piecewise functions fitting with RMS weighting. The random term with stationary random characteristics was based on Parseval theorem to establish the expression of random harmonic function, and the two component expression functions were reconstructed to realize the expression of its parameterized test load model. Through the test data of small sample loader, the validity of the parameterized test load model for typical shifting condition reconstruction and its non-stationary random characteristics and non-stationary random correlation were verified, which can be used as a load expression for the transmission drive shaft bench test of the typical shifting condition of the loader. The modeled method had engineering value for test bench load reconstruction under non-stationary random cyclic loading conditions.