The invention relates to a machining process, in particular to a processing method for a phi 52H7*850 deep hinge pin keyhole at a matched position of parts of different materials. The processing method comprises the following process steps of: (1) performing center drilling; (2) drilling a phi42*150mm process hole; (3) boring the phi42*150mm hole into a phi45H8*100mm hole; (4) drilling a phi45*160mm hole; (5) drilling the phi42*150mm process hole to deepen the process hole to be phi42*260mm in dimension; (6) boring the hole to be phi45H8*250mm in dimension; (7) drilling the hole to be phi45*420mm in dimension; (8) boring the hole to be phi48H6*50mm in dimension; (9) installing a guide sleeve and finely boring the hole to be phi48H6*400mm in dimension; (10) drilling the hole to be phi48*860mm in dimension; (11) boring the hole to be phi51.5H6*850mm in dimension; (12) boring the hole to be phi51.7H6*850mm in dimension; and (13) finely boring the hole to be phi52H7*850mm in dimension. By adopting the front boring and rear supporting gradually deepening processing method, the high-accuracy deep hole processing at the joint of two materials is realized, and the assembly accuracy problem of a large-sized transmission part is solved. The processing method is mainly used for processing the hinge pin keyhole between a large-sized flywheel and a main shaft.