Different from the concentrated load, the sliding bearing-wind turbine gearbox coupling interface load is a time–space coupling distributed dynamic load that need to be represented by variables in both temporal and spatial dimensions. In order to apply directly the general shafting transient response method based on concentrated load to analysis transient response of sliding bearing-wind turbine gearbox, a decoupling method for coupling interface load based on POD decomposition algorithm was established to address the spatiotemporal coupling characteristics. In which coupling interface load is decoupled into several sets of space–time independent sub-distributed loads composed of time history and spatial distribution function. The Chebyshev polynomial is used to transformed the spatial distribution function into the concentrated load acting on the limited action point of the shaft system. The improved method is verified by comparing with the results coming from finite element software.