Abstract: The stability of a quadruped walking vehicle are studied. A theorem is proved which can reveal the essence of walking of a quadruped. Based on the theorem, such conceptions as critical phase, critical line, critical point and critical state are proposed, which application to the reseach on the stability of quadruped is introduced simply.

Key words: 步行机构, 临界状态, 稳定, Fatigue, Micron copper wire, Size effect