The invention puts forward a stone material surface roughness on-line detection device and a stone material surface roughness on-line detection method, and belongs to the technical field of stone material surface quality detection. The device comprises a base, a liftable bracket, a camera, an enlarger lens, a circular light source, a camera obscura, a positioning device, an image acquisition card, and a computer. The method has a simple process, and is easy to operate. Problems such as low precision and unstable detection caused by subjective factors and proficiency are overcome. An optical technology, a computer technology, a digital image processing technology and an on-line precision measurement technology are integrated. The surface glossiness of a stone material can be detected online, the detection result can be fed back to a detection system in real time, and stone roughness detection can be completed automatically. A plurality of problems of stone enterprises, such as low detection efficiency and unstable detection, are solved effectively.