The invention discloses a cover plate opening device of a work well. Wedge-shaped openings for supporting a spandrel girder are formed above two spandrel girder supporting seats correspondingly, the spandrel girder is fixed to the spandrel girder supporting seats, and a long hole linking up the upper surface and the lower surface of the spandrel girder is formed in the spandrel girder so as to allow a pull rod to penetrate through; vertical type through holes for mounting guide columns are further formed in the spandrel girder supporting seats, a base is arranged below the spandrel girder supporting seats, jacks are arranged between the base and the spandrel girder supporting seats, and the guide columns are arranged on the base and upwards penetrate through the vertical type through holes of the spandrel girder supporting seats; and the lower end of the pull rod is provided with a flat structure, the upper end of the pull rod is provided with outer threads, a through hole allowing the pull rod to penetrate through is formed in a positioning plate, after penetrating through the long hole in the spandrel girder, the pull rod is positioned by using the positioning plate, and then locked by using a nut. The cover plate opening device of the work well can achieve rapidness, time saving and labor saving, and safe opening of the cover plate device so that the construction work under the well can go on smoothly.