The flame characteristics of biodiesel burning in industrial furnace were studied. The volume, shape, structure of flame and length were analyzed based on image processing by using high-speed photography method. The experimental results showed that with the increase of excess air coefficient α, the volume of flame gradually decreased and the flame deformation was more and more serious. With the increase of atomization pressure p, the volume of flame first increased and then decreased. The flame deformation was more and more serious, and the flame structure was more and more fragmented. Through the calculation, the range of the actual length of the flame of 0.2s was very large, which emerged a sudden increase and drop rule, existed a “taking off the flame” process. The flame length became inversed to the excess air coefficient α. Along with the decrease of the atomization pressure p, the curve of flame length changed gently.