Plane wave expansion method was applied to investigate the band gap properties of a proposed thermo-magneto-mechanical phononic crystal nanobeam with surface effects. Numerical results and further analysis demonstrate that band structure was indirectly affected by the influence of operating temperature on Young's modulus of epoxy. Magnetic field had more effects on the band gaps of higher orders than lower orders. The influence rules of pre-stress were similar to magnetic field, but singular pre-stress appeared, which was bad for the opening of band gaps. With the increase in operating temperature or magnetic field, the value of singular pre-stress increased. In addition, the influences of surface effect and geometric parameters on band gaps were also studied in detail. Collectively, our results are expected to be helpful for the design of thermo-magneto-mechanical nanobeam-based devices.