The invention relates to the field of mechanical parts, and discloses a spline combination sequence selection method for prolonging service life of a spline and a spline assembly. The selection methodis characterized in that the influence of spline machining errors and the combination sequence on the load distribution on spline teeth is considered, a maximum nominal tangential force of the splineteeth in each combination sequence can be really calculated, and the optimal combination sequence of the splines can be reasonably obtained; and under the combination sequence, the maximum nominal tangential force of the spline assembly is minimum, the performance is more stable, the service life is longer, the reliability is higher, and the spline assembly can bear larger loads. According to themethod, the spline assembly is assembled according to the optimal combination sequence obtained by the selection method, the spline assembly can bear larger loads, the performance is more stable, theservice life is longer, and the reliability is higher.