Abstract: Up to now, there is no one mature and valid method to solve the problem about prediction of block collapse geological hazard during construction of tunnel in jointed and block rock masses. By gathering rapidly geological information exposed during excavation, the authors combined the discontinuities 3-D network com-puter simulationwith ShiGenhua's block theory, established a 3-D geological model of jointed and block rock masses, and developed a program of seeking unstable rock block. This method had been used to predict block collapse geological hazard in ShiBeilin tunnel successfully and obtained satisfactory results.