The invention relates to the field of axle assembly, and discloses a cushion selecting method and device for an integrated-type axle main transmission system. The method comprises the steps: S1, assembling a main transmission assembly outside a main transmission cavity, enabling the main transmission assembly to meet the requirements of an engagement state and to have the needed pre-tightening force, and measuring the actual size of the main transmission assembly; S2, measuring the installation size of the main transmission assembly; S3, calculating the size of the thickness of a needed cushion according to the installation size of the main transmission assembly and the actual size of the main transmission assembly, and selecting the needed cushion according to a calculation result. The method is directly used for measuring the main transmission assembly which meets the requirements of the engagement state and has the needed pre-tightening force, carries out the parameterized cushion selection, is high in reliability, is simple in operation, is low in production and manufacturing cost, and is great in economic benefits.