The utility model discloses an online temperature measurement device for a vertical fire path of a coke oven. The online temperature measurement device comprises a lens cone, an adjustable reflection barrel, a sealing pressing ring, an objective lens adjusting ring, an objective lens pressing ring, a reflective lens gland, a reticle pressing ring, a protective glass pressing ring, a jackscrew, an optical-fiber flange, a seal lens, an adjective lens, a reflective lens, a reticle, a piece of protective glass and washers. According to the online temperature measurement device for the vertical fire path of the coke oven, the positions of the parts are adjusted in a laboratory in advance, then the parts are quickly and directly assembled in situ, and the online temperature measurement device is in communication with a far-end control room through optical fibers, thereby avoiding the negative influence on temperature management due to temperature measurement sites, temperature measurement time points, manual operations of measurement personnel and the like, and improving the accuracy and reliability of the temperature measurement. In addition, the mechanical device is stable and reliable and is good in sealing performance, so that the long-term stability of a light path is ensured, the distance coefficient is large, and the measurement precision is high.