Abstract: Three 3D morphology parameters independent of measurement scale within limits are introduced to characterize the morphology characteristics of rock joints, and a new peak shear strength criterion for the rock joints is developed based on the morphology parameters. Then, both the new criterion and Barton’s criterion are adopted to calculate the peak shear strength of 23 pairs of rock joints. By comparing the calculated and tested peak shear strengths, the new criterion is proved to be more reasonable, while the peak shear strength calculated by Barton’s formula is underestimated. The new criterion has a clear physical meaning because the contribution of different morphology characteristics to the peak shear strength is represented in detail by the three morphology parameters, and it is also convenient for the new criterion to be applied to engineering practice since the morphology parameters can be measured by any scale within some limits. Furthermore, the new criterion is essentially the generalized 3D form of Patton’s criterion as it can be simplified to Patton’s formula when applied to regular joints.