Abstract: Based on the rock joint characteristics of the Gaozhushan tunnel in Yushan county, a 2D calculation model is established using the discrete element software UDEC, and the effects of the joint dip angle and joint spacing on tunnel deformation under two sets of joint couplings is studied by calculating the vault collapse heights in different conditions. Results show that by increasing the joint dip angle, the collapse height decreases (30° to 45°) after initially increasing (0° to 30°), and then increases again (45° to 90°); the calculated collapse height is closest to PU's theoretical value when the dip angle is 60°; and with an increase in joint spacing, the collapse height decreases nonlinearly. When the joint spacing is 0.2~1.0 m, the collapse height can be calculated with equation (1) and the calculated value is closest to PU's theoretical value when spacing is no more than 0.2m.