The study of mechanical property about low-dimensional materials with its wide application has been one of the hot-spots. In the real-strain measurement of low-dimensional materials,the tracking target on the surface of large distance specimen would move out the scope of image tracking. In this way,the tracking target might be lost,which affects the real-strain measurement. So the optical extensometer based on digital image tracking technology is proposed to change the large distance to small one. Then,the tracking objective is adjusted to move in the screen field of view. The method of real tracking can be realized. Moreover,the strain regulation of low-dimensional materials might be dynamically learned. The strain measurement is carried out using micro-mechanics universal testing machine and optical extensometer together. From the experiment,the results obtained by the optical extensometer are agreed with ones obtained by the micro-mechanics universal testing machine. And,the objective is orientated in the 0.01 pixel location using the arithmetic of bilinear inter value. So,the optical extensometer can be applied on the real-strain measurement of low-dimensional materials. Also,a new experimental method is offered for studying the dynamic mechanics of low-dimensional materials.