Fire detection based on sequences of images is more suitable for the need in big room or badly environment. Color and contour are both the important features of a flame image. The method to extract the contour feature of a flame image is developed based on threshold of flame area. The edges of the burning flames jitter continuously, but their contour are similar each other. The method to detect flames in video sequences is proposed here based on flame’s dynamic contour. Many experiments show that the system is able to work well and get high detection rate with a low false positive rate.