Voting is usually used in democratic society for decision-making, but majority circle is inevitable, if choosing that method. It is complex to by combinatory to compute the probability of majority circle, instead of that, geometry is an intuitive and simple method, besides, it can show the relationship between the different combination and majority circle. First, compute the probability of majority circle by combinatory, and then denote candidate triangle and result-profile triangle. Finally analyze each preference combination and its voting result, what’s more, if voting majority circle occurs, compute the probability.