Damage in the rock will deteriorate under the water-rock interaction. This paper focuses on the destabilized damage state of muddy siltstone under different water content states. Nonlinear buttress loading splitting experiments were conducted, and acoustic emission equipment was used to analyze the results. The study reveals that: (1) The evolution trend of b-value and S-value in the five stages of rock damage exhibits distinct stage characteristics. (2) The acoustic emission evolution characteristics of rock samples in different water-bearing states during various stages exhibit certain differences, and the rock samples deteriorate significantly when the water content exceeds 1. 0458%. (3) The sudden climb of b-value and the sudden jump of S-value can be considered as the precursor characteristics of the instability of pulverized sandstone damage. (4) The principal structures of rock samples in two water-bearing states are derived based on the continuous damage medium mechanics, and the rationality of the theoretical curves is verified with experimental curves. The acoustic emission characteristics and damage evolution laws of the rock samples can serve as a reference for monitoring the stability of the rock body during water influx in tunnels.