To reveal the rock breaking characteristic of disc hob under true triaxial condition, the Drucker-Prager strength theory, CSM model and intermediate principle stress coefficient β were used to establish a theoretical calculation model and a simulation analysis model, which can be used to study the fracture characteristic of rock and the stress characteristic of hob under high ground stress. The results show that the extreme value of vertical force decreases remarkably after rock is damaged, while the range of rolling force and lateral force changes little. The lateral force is always smaller with constantly changing direction, leading to the vibration and uneven wear for cutters. With the increase of intermediate principal stress effect, the number of crushing elements decreases exponentially, and the maximum force in vertical, rolling, and lateral directions increases exponentially, in which the increase of the lateral force is the smallest. With the increase of penetration, the number of crushing units and the rock breaking force increases simultaneously, and the increase extent also becomes larger, in which the increase of the lateral force is the largest. The relative errors among actual values, theoretical calculation values and simulation results are very small, which can verify the reliability and accuracy of the theoretical model and simulation model.