The invention belongs to the field of gasifier safety techniques and particularly relates to a visual flame detection system of a gasifier, which comprises detection probes arranged on a furnace body, wherein the detection probes are used for acquiring image or video information in the gasifier and outputting the image or video information to data acquisition control cabinets through cables; the data acquisition control cabinets are used for performing analog-digital conversion of the received image or video information and outputting information to a server through cables or optical cables; and the server is used for processing the received information to obtain and display flame temperature field distribution and video images. Meanwhile, the invention further discloses a control method of the system. The detection probes are arranged to directly acquire the image or video information in the gasifier and then output the image or video information to the server for display, so that the working condition of combustion in the gasifier can be seen conveniently and visually. Besides, the server is used for processing the images or video information to obtain the flame temperature field distribution image, so that the combustion intensity of flame in the gasifier can be known quantificationally.