A novel method based on space-time image features is proposed for automatic behavior modeling and recognition. The method is composed of the following three steps: (1). Video sequences are converted into a space-time image, and the image is divided into equal length segments; (2). From these segments, an unsupervised technique based on Dynamic Time Warping is used to determine the groups of different behaviors; (3). The behavior templates are built according to these groups, and are used for the recognition of behaviors. The method does not need to track the body parts and can model the behaviors without any prior knowledge. Experiments also demonstrate the effectiveness of our new method.