The invention provides a modality optimization method of an outside rear-view mirror of an automobile, and belongs to the field of automobile part optimization. The modality optimization method comprises the following steps: executing a rear-view mirror mounting point optimization step and a rear-view mirror body optimization step; assembling rear-view mirror body finite element models onto an automobile door welding piece and a hinge assembly finite element model; calculating a rear-view mirror assembling modality, judging whether the rear-view mirror assembling modality achieves a target requirement or not, if the rear-view mirror assembling modality achieves the target requirement, setting the rear-view mirrors and the rear-view mirror mounting points according to the modality, and otherwise, carrying out further optimization and/ or topography optimization. The modality optimization method has the beneficial effects that the arrangement of the rear-view mirror mounting points is optimized at the initial stage of project development, CAE (Computer Aided Engineering) is involved into a project development stage as early as possible so as to be favorable for shortening development time and realizing node control; and the modality optimization method is suitable for all automobile types and rear-view mirrors, an operation method is simple and practical, time for repeated optimization can be saved, and restraining restriction that traditional design depends on experiences can be put an end.