本論文探討機器人腳與地面的接觸行為以及傾倒問題，利用有限元素軟體ANSYS求出機器人腳受到腳踝施加的正向力時所受到的應力分佈，以及同時受到正向力與力矩作用時，機器人腳與地面接觸面積的變化。當機器人腳所受力矩使接觸面積僅剩最後一小區域時，即成為即將傾倒的臨界狀態。本研究先以球對地面的接觸問題進行分析，得到的數值結果接近赫氏接觸解析解，再以此方法來分析機器人腳與地面的接觸問題。分析過程分為兩部份，第一部份進行未施加力矩的接觸分析，求出受到正向力作用之下的接觸節點以及應力分佈。第二部份是在原有的正向力之外並同時施加力矩，並逐漸增加力矩以求出造成臨界狀態的力矩大小。本論文分別針對機器人腳底邊緣有導角以及無導角的情況進行分析。 In this thesis the stability of a robot is investigated by considering the foot-to-ground contact. Finite element software ANSYS is used to obtain contact stress distribution when the foot is only subjected to its own weight, and obtain the contact size when a turning moment is also applied. The contact size decreases with the increasing moment, until a critical state is reached in which only very few nodes are still in contact. The ball-to-ground contact is first performed to check the solutions with its Hertz solutions. Then the foot-to-ground contact is performed in two steps. Firstly the foot is only subjected to a normal force, and then a moment is also applied, so that the moment to bring the foot to the critical condition may be obtained. In this thesis we deal with a robot foot with a radius at the edge and a foot with no radius.