This paper presents a probability method for detecting people in a static image. We simplify people as a torso and four limbs. The torso is fitted by a quadrangle, and each limb is fitted by one or two quadrangles depending on its pose. In order to find people, we should try to find a combination of quadrangles that must satisfy some geometric and topological constrains. Firstly, we try to detect and fit rectangle regions in the image, then we search some combinations of rectangles under certain constrains. After we get a combination, we calculate its probability of being people. If the probability is above threshold, we adjust the vertexes of rectangles so as to get a compact people model.