A photoelectric gas sensor based on micro-cantilever projection comprises a non-transparent rectangular shell (9), a chip encapsulated on the bottom of the rectangular shell (9), and a light source (8) fixed to the upper portion of the side wall of the rectangular shell (9), wherein the chip is composed of a substrate (1), a lower insulation material layer (2), a light-sensitive material layer (3) and a micro-cantilever structural layer (5). The photoelectric gas sensor is characterized in that the middle of the micro-cantilever structural layer (5) and the middle of an upper insulation material layer (4) form a through rectangular cavity, a rectangular mass block (7a) in the rectangular cavity is connected to the cavity wall, close to the light source (8), of the micro-cantilever structural layer (5) through a strip-shaped micro-cantilever (7b) to form a special-shaped micro-cantilever, and a gas-sensitive material layer (7c) is deposited on the surface of the rectangular mass block (7a). The photoelectric gas sensor is high in sensitivity and resolution ratio, quick in response, low in cost and long in service life.