Abstract: By using the electro-hydraulic servo rock testing machine of TAW-3000 and the fully digitized acoustic emission(AE) monitoring system of PCI-2, Brazil disk splitting test is carried out on three kinds of pelitic siltstones with different water-bearing states, and the characteristics of mechanical and AE under three kinds of water-bearing states are obtained.The test results show that the three kinds of water-bearing argillaceous siltstones undergo pure mode-Ⅰ fracture under the split tests.Under the influence of the mode of argillaceous diagenesis, the softening effect of the rock is obvious.The average tensile strength of the water-saturated argillaceous siltstones is less than 39.71% under the dry condition.During the evolution of rock mode-Ⅰ faults, AE activity of saturated rock samples is restrained, and energy release is weak during loading.In addition, high frequency dominant frequency appears in dry state and low frequency dominant frequency appears in saturated state before rock breaks.With the increase of water content, the main frequency band near 100 kHz decreases gradually, and the distribution gradually concentrates to the middle low main frequency band.It is noteworthy that the evolutionary regularity of the 20 kHz and 50 kHz middle and low main frequency bands “from very few distribution to centralized occurrence and then to gradually disappear” can be used as the sensitive frequency band for the mode-Ⅰ fracture test of argillaceous siltstone.