The invention discloses a photovoltaic module automatic trimming method and a trimming machine. The rimming machine comprises a cutting part and a cleaning frame; the cutting part comprises four guiding shafts for defining a frame shape; a movable scraper device is mounted on each guiding shaft; two opposite cutters are mounted on the end, facing a to-be-trimmed assembly, of each scraper device; and the cleaning frame is positioned below the cutting part. By performing automation of the production line, the assembly production efficiency is improved, the mechanical trimmed edge is tidy and attractive, and the appearance can reach the A level demand; potential safety hazards caused by manual trimming can be eliminated; whether the trimmed edge is tidy or not can be detected automatically, and the cutting and trimming operations can be performed repeatedly, so that product precision is improved; and after the redundant back plate and EVA film are cut off, the materials fall off to the cleaning frame below the mechanical equipment, so that cleaning can be performed conveniently.