Abstract: In view of the engineering phenomenon that red-bed mudstone is prone to complex and variable disintegration under the influence of water and heat factors, taking the medium-weathered red-bed mudstone as the research object, static immersion and water-heat cycle tests were carried out to obtain the characteristics of the morphology and particle composition of the disintegrates changing with immersion time and the number of water-heat cycles, and further explore the disintegration laws of red-bed mudstone under static immersion and water-heat conditions.The experimental results show that under the condition of static immersion, the initial stage of disintegration is dominated by surface debris shedding, and with the development of cracks to penetrate, the fracture is fragmented block. This process was basically completed and stabilized within 1 d, and the crushing effect became weak subsequently. The disintegrations were mainly 20-40 mm particles, and the percentage content was more than 60%. An followed by 10-20 mm particles, the percentage content was 20%-30%. The gradation curve of disintegrates changed little. Under complex hydrothermal conditions, the disintegration process is divided into two steps. One is that large mudstone is broken into irregular particles, and the other is that irregular particles are gradually rounded, and large particles continue to collapse. After the first cycle, the particles larger than 20 mm are disintegrated by 90%. As the number of cycles increases, the particles larger than 5 mm decrease gradually. The disintegrate gradation curve change obviously. This study reveals the disintegration characteristics of red-layer mudstone under static immersion and hydrothermal conditions, which is expected to provide guidance for the prevention of disintegration of red mudstone in engineering practice.