An efficient geological logging method is urgently needed in the tunnel construction. CCD digital geological logging system is introduced into the geological investigations in the construction of the tunnels on the passengerdedicated railways in China. In the paper, the principle and method of CCD digital geological logging system are presented and engineering practice of geological logging and rock mass grading is conducted. Furthermore, the problems of CCD digital geological logging system are pointed out and the prospect of the application of CCD digital geological logging system in the geological investigation during tunnel construction is provided.