The invention discloses a sheet metal bending device and a bending method. The sheet metal bending device comprises a base, wherein an inverted L-shaped support is fixedly mounted on one side of the top of the base, a hydraulic cylinder is fixedly mounted at the top of the inner wall of the inverted L-shaped support, a mounting groove is formed in the middle of the top of the base, a second rotating motor is fixedly mounted in the mounting groove, and the output end of the second rotating motor is fixedly connected with a second rotating shaft. According to the sheet metal bending device and the bending method, through the corporation of a circular rotary plate, a bending device, a lower mold base, the hydraulic cylinder, an inlet-outlet opening, an upper mold base, a limiting block, a limiting rod, a spring, the second rotating shaft, the mounting groove, the second rotating motor, a storage groove and a forming cavity for use, the working intensity of workers is greatly reduced, andthe sheet metal bending efficiency is improved; and meanwhile, the storage groove can define the position of a metal plate, so that shifting of the metal plate before the metal plate is bent can be avoided, the sheet metal bending quality is improved, and the workers can conveniently place the metal plate.