The invention provides a device and method for detecting the size of a silicon briquette. The device for detecting the size of the silicon briquette comprises a first laser generator arranged on the left side of a conveyer belt, a second laser generator arranged on the right side of the conveyer belt, a third laser generator arranged above the conveyer belt and a processor, wherein lasers emitted by each laser generator are perpendicular to the corresponding surface of the silicon briquette, and the processor is connected with each laser generator. The processor is used for obtaining a first electric signal, a second electric signal and a third electric signal respectively, the first electric signal is generated when the lasers emitted by the first laser generator are blocked by the silicon briquette, the second electric signal is generated when the lasers emitted by the second laser generator are blocked by the silicon briquette, the third electric signal is generated when the lasers emitted by the third laser generator are blocked by the silicon briquette, the width of the silicon briquette is obtained through calculation according to the first electric signal and the second electric signal, and the height of the silicon briquette is obtained through calculation according to the third electric signal. By the adoption of the device and method for detecting the size of the silicon briquette, the size can be detected without the need for making contact with the silicon briquette, and the problem of edge breakage caused by contact measurement is avoided.