The invention discloses a device for monitoring sheet surfaces. The device comprises a work platform provided with a transfer tank. The transfer tank is provided with a primary conveyor belt, a secondary conveyor belt and a three-stage conveyor belt, wherein the conveying speed is sequentially increased. A monitoring box is arranged above the secondary conveyor belt. The monitoring box is providedwith a feeding port and a discharging port running through the conveying direction of the secondary conveyor belt. A vertically arranged image magnifying device is connected to the top surface of themonitoring box. The image magnifying device comprises a crystal glass body with a vacuum chamber inside. The vacuum convex cavity is provided with a layered intermediate thickness and a thin edge anda transparent convex mirror. Compared with the prior art, the device for monitoring sheet surface has the following advantages: the design is reasonable, and the structure is simple; the sheet surface can be enlarged and refined, which is convenient for observation, so as to find the defects on the sheet surfaces in time; and the range of concentrating can be adjusted, and at the same time automatic feeding can be realized without manual handling.