In the petrofabric study，generally only after the rake direction and rake angle of the optic axis of quartz in thin section of rock and mineral are determined on the universal stage, a stereographic . projection diagram of the optic axis of quartz can be made. However, our method is put forward on the principle that the extinction directions of the same optic axis of quartz on a succession of two different planes result in the intersection of these planes, and the intersecting line must be the optic axis. This method, therefore, requires only determining two extinction directions and a rotation angle of I·axis of each quartz grain on dif f erent planes，a projection diagram of the optic axis can be made. The projection is made on our designed projection net for the extinction direction method according to the readings of N·ring，I-axis and M-ring. It has been proved from practice for several years that this determination Ineth,od is an easy, ready and accurate one in the petrofabric work.