Abstract: The fracture criterion of wood flour is proposed based on the experimental and theoretical results from the dried larch sawdust. The fracture morphology and size of the different mesh sawdust were observed by the microscope in the preparing process of the dried larch sawdust into wood flour. The experimental result shows that the 0.08 mm wood flour mostly is in the form of sticks and includes the pits and arbitrarily arranged filaments on the radial wall of the tracheid observed clearly after enlarged 40 times. The experimental phenomenon presents that the main reason resulting in the fracture of the sawdust grain is the initiation and propagation of the crack in the sawdust grain. The interactive mechanism between cracks in the sawdust grain during the fracture process of sawdust was investigated by using the theory of fracture mechanics and the experiment results. The fracture criterion of the sawdust grain was obtained based on the interactive mechanism and a fundamental assumption that the dried sawdust is the brittle plate layer material.