Aiming at the difficulties of real-time measurement of the actual size of the flame in fuel combustion process, a non-contact testing system was developed to achieve the real-time measurement of the flame size based on virtual instrument platform. The system uses a USB1080P HD camera to capture flame image in real time, set region of interesting for flame image, process the image and extract the edge of flame. The establishment of the relationship between actual size and pixels is based on the dot reference diagram, and the system can access the real size of the flame in real time. Experimental results show that the system can quickly realize the measurement of the flame size, graphical display, data storage, real-time observation of the flame size change, and web publishing.