The invention discloses a mechanism capable of achieving irrational rotation of an upper polishing disc. The mechanism comprises the upper polishing disc, a lower polishing disc, a mounting base, a supporting base and a rotating shaft; the upper polishing disc is fixed to one end of the rotating shaft which is supported on the supporting base, the lower polishing disc is mounted at the position, below the upper polishing disc, in the mounting base, and the mechanism further comprises a first planetary gear train, a second planetary gear train, a universal shaft joint and a drive motor; the mechanism is simple and compact in structure and low in production cost, on the grinding machining kinematic principle, the scientific problem of machining track line circular closing can be solved, and compared with machining precision of a traditional rational rotating speed drive device, the precision is greatly improved; meanwhile, irrational numbers of different multiples can be achieved during rotation of the upper polishing disc, and the application range of the device is greatly improved.