Abstract: Many theoretical criterions have been proposed to predict the shear strength of intermittent joints, of which the Jennings criterion is widely used. In Jennings criterion, the mechanical parameters of joint and rock bridge are simply averaged by a weight coefficient called connectivity rate to calculate the peak shear strength. The main limitation of Jennings shear strength criterion is that it cannot consider the mechanical weakening of rock bridges during the shear tests. The theoretical results by Jennings criterion are usually not consistent with the measured ones. A modified criterion is put forward. The modified criterion can overcome the limitations because it takes the mechanical weakening model of rock bridges. The results show that the predicted values by the modified Jennings criterion is closer to the measured data, compared to the original Jennings criterion, which indicates that the new criterion is better. Finally, the limitations of this new strength criterion are also analyzed.