The micro-tensile processes of Chinese-fir and Masson pine are studied by synchrotron radiation light (SRL). It shows that the patterns of crack propagation are different in tangential and radial tensile process. In the tangential tensile process

because of stress concentration near the crack

once the wood forms a crack

more cracks will occur. In the radial tensile process

crack appears in the standard specimen first mainly in the boundary of early wood and late wood. Usually it extends to early wood. Crack tip does not propagate under tension parallel to grain when the pre-cut crack is perpendicular to grain. On the contrary

small cracks perpendicular to grain form and gather near the pre-cut crack. Obviously sliding between tracheids and intercell failure is easier to happen than transwall failure.