The invention relates to a coupling method of an optical receiving sub-module of an optical module. The coupling method comprises the following steps: S1, fixing a TIA, a PD, a DMUX and an adapter on a shell; S2, powering up the TIA and the PD through golden fingers of the shell, connecting a light source through an adapter, and arranging a glass block between the adapter and the DMUX; s3, selecting one path for coupling, fixing the position of one first lens in the light propagation direction of the path firstly, and then adjusting the position of the first lens; s4, adjusting and determining the position of a second lens between the adapter and the glass block; s5, removing the auxiliary coupled glass block, and arranging a third lens, an SOA and a fourth lens on the glass block; and S6, sequentially adjusting and determining the positions of the other first lenses. In the initial stage of coupling, the glass block is adopted to translate an optical path to replace the third lens, the SOA and the fourth lens for coupling, and the glass block is equivalent to the third lens, the SOA and the fourth lens, so that the coupling process is simplified.