Abstract: Based on high speed rideo technology and image recognition technology, instananeous images of chip flow in the milling of wood based materials were collected and processed. The changes of the formation mechanism, the flow speed and diffusion angle of chip flow were analyzed by ProAnalyst Software. The results indicated that the formation procedure of the chip flow was divided into two stages. First stage was that the material of the cutting layer went away from the workpiece, and began to form the chip flow before touching the tooth gullet. Second stage was that the chip flow went away from the tooth gullet, and diffused in the air. The variety of chip flow speed was also divided into two stages. First stage was that the chip flow with a certain velocity from the work piece began to become reduced. Seconde stage was that the speed of the chip flow reached the peak value, and then trended to reduce in the air. When milling the wood based materials, the cutting tool was not in a stable rotation speed, with the tooth cutting in the workpiece, the speed of the tooth decreased to minimum value until the tooth got away from the workpiece. At this very moment of the tooth getting away from workpiece, the speed quickly restored and kept stability. Diffusion angle of chip flow would decrease with the increase of cutting speed.The diffusion angle of fiberboard milling is the biggest during the wood based materials milling in the range of 533°—665°.