In the process of tunnel construction, knowing the distribution and connectivity of cracks in surrounding rock around tunnel is crucial to select reasonable construction methods and supporting schemes. Based on the requirements of tunnel construction, a threedimensional fractures model for rock masses is established and the connectivity of fractures is analyzed. Based on the distribution laws of parameters of insitu fractures, Monte Carlo simulation is adopted to generate threedimensional data for fractures, which are represented by spatial thin disks and then the threedimensional model for fractures is formed. Compared to the test data from vertical drillings, the proposed model is modified (screened) to accord with the actual situation. Then, by using the principle of space geometry, the connectivity of fractures is analyzed through the interrelationship between two disks. After that, C++ is used to realize the calculations in the connectivity analysis. The paper presents a method of connectivity analysis for analyzing the interrelationship between any two disks and realizing the connectivity analysis of cracks.