The invention discloses a method for identifying and detecting the fire flame in a big space, including: pretreating the input video streams, performing movement detection for the video streams to obtain the movement pixel, performing color detection for the video streams to obtain the pixel with the flame characteristic color, performing frequency domain analysis for all the pixels according with the movement detection and the color detection flame characteristic, searching the communicating areas formed by mutually connecting the pixels according with the same characteristic, calculating the circumferences and the areas of the obtained communicating areas to perform the shape analysis, performing the area change variable analysis for each communicating area, at last judging whether the fire happens. In the method, the real flame in the big space is distinguished from the flashy car light, so that the device is not only for the flame detection in the tunnel, but also used in the big-space fire flame detecting sites such as a gymnasium, a museum, a warehouse and the like.