The invention discloses a plane arc imaging and spectrum synchronous acquiring device. The device comprises a liftable worktable, a plane arc imaging system, a spectrometer, a high-speed camera, a trigger device and a computer; the plane arc imaging system, the spectrometer, the trigger device and the computer are all placed on the liftable worktable; through adjustment of the height and the position of the liftable worktable, after radiation generated by welding arcs enters the plane arc imaging system for light separation by the plane arc imaging system, one part of arc radiation enters thespectrometer, and the other part of arc radiation is acquired for imaging through the high-speed camera; and a signal output end of the trigger device is connected with external trigger interfaces ofthe plane arc imaging system and the spectrometer. The device reduces the damping influence of optical fiber transfer or optical imaging mirror sets on spectrum acquisition to the greatest extent whenthe acquiring precision and the resolution of the spectrometer are guaranteed, and realizes scanning of spectrum information in a whole arc plane within possibly shorter time.