Abstract：Digital photography technique is an important method to obtain information of tunnel face in constructing rock tunnel construction with new Austrian tunneling method(NATM). There are lots of dust and fog in constructing rock tunnel with NATM，and the illuminance is always insufficient and uneven since the diameter of dust is much longer than the wavelength of visible light wave but close to infrared. According to the principle of diffraction，visible light could not go through the dust but infrared rays could do. So it is hard to take clear pictures of tunnel face with classical photography technique but possible by infrared photography technique in tunnel construction. The application of infrared photography technology to taking picture of tunnel face for constructing rock tunnel is specified. The possibility and superiority of this method are proven by analyzing in-situ experiments；and the characteristics of infrared photographs of tunnel face are also analyzed aiming at image processing of denoising-illuminance equilibrium-threshold division. In the image recognition step，the Hough transform is used to identify the linear feature of tunnel face picture；and the validity of this method is proven by comparing the recognizing result with monitoring data. Experimental results show that infrared photography is helpful for getting clear tunnel face photograph in rock tunnel construction with NATM：the image processing overcomes the problems of image noise，the overexposure，underexposure in the circumstance of poor illuminance. The recognition of linear feature is on the basis of 3D numeral reconstruction and could provide some critical parameters for rock masses classification.
