The little frequency difference of beat vibration was analyzed. By using multi-dimensional figure method, its experiment was conducted. The upper and lower amplitude limits, and the fundamental frequency were derived by extend i ng the traditional two-beat theory to multi-beat theory. The theoretical results were verified by the simulation analysis. A multi-dimensional figure method was presented, and the two-beat Lissajous figure and threebeat torsion-string-area figure were derived and analyzed. It was found that the Lissajous and torsion-st ring-area figures were sensitive to the minor frequency difference. The beat exp er iment of plane blade was carried out. The theoretical results of the upper and l ower amplitude limits and fundamental frequency agree well with the experimenta l results. The multi-dimensional figure method is effective on real-time obse rvation and analysis of the little frequency difference vibration.