High-energy beam polishing method shows a promising development prospect owning to its non-contact finishing process. In this work, the polishing abilities of micro plasma beam were verified, and AISI 304 stainless steel was chosen as the experimental material. To achieve a multi-aspect investigation of the finishing effects after micro plasma beam treatment, the change regularly of surface morphology, nano-mechanical property and microstructure under the different number of passes was found. The results indicated that the surface roughness could decrease from 5.11 +/- 0.55 mu m to 0.41 +/- 0.05 mu m when the number of passes was 3. When the maximum load was 4000 mu N, the nano-hardness and the elastic modulus of treated specimens could be increased to 3.01 GPa and 87.77 GPa respectively. The microstructure was refined and the average grain size in the molten pool could achieve 3.48 mu m, while the average grain size in the base was 17.41 mu m. Moreover, no chemistry modification of the treated area was found. It can be concluded that the micro plasma beam is capable of achieving surface polishing with the improvement of mechanical properties.