The deformation experiments of three kinds of coal samples whose Rmaxo is D.67%. 3.41% and 4.90% respectively were done with the Griggs’type high temperature and confining pressure rock experimental deformation aparatus of phyropyllite medium under conditions of t=350-700℃, Pc=400-600MPa,ε=10%-30%,ε=3.63×10-6-2.59 ×10-5s-1. The experimental results show that:(1)The origin of vitrinite reflectance optical fabrics is caused by the reorientation of graphite-like aromatic lamellae under tectonic stress. The major mechanism for the reorientation of aromatic lamellae is preferred neucleation and growth in the favorable direction with the increase of aromaticity during coalification. and the mechanism of physical rotation may also exist, but the possibility of mechanism of intragranular plastic deformation of molecular is very little.(2) The reorientation of aromatic lamellae takes place dominantly in the stage of relatively low coal rank. The Z axis of VRI mainly reflects the direction of tectonic compressive stress in this stage.(3) Feartures of VRI’s shape not only are related with the condition of finite strain, but also depend on the variation of aromaticity in vitrinite to a great extent.VRI can not reflect the features of finite strain ellipsoid and the magnitude of strain in the stage of higher coal rank. Therefore VRI can not be directly used as markers for strain analyses, only under some specific conditions may it be used to approximately estimate some features of strain ellipsoid in the stage of relatively low coal rank.