Deformation experiments were carried out on three kinds of coal samples, with R m a x ° 0.67, 3.41, and 4.90%, were performed in a Griggs' type high-temperature and confining pressure rock deformation apparatus of phyropyllite medium at 350-700°, 400-600 MPa. The experimental results show that vitrinite reflectance optical anisotropy is caused by the reorientation of graphite-like aromatic lamellae under tectonic stress.