Abstract: Fracture extension of silty mudstone under hygrothermal action is an important factor leading to silty mudstone slope failure. Focusing on the fracture extension of silty mudstone, conduct hydrothermal alternation test and Brazilian splitting test, analyze the fracture development law in the whole process and the difference of fracture development in the wetting and heating process, investigate the influence of hydrothermal alternation and fracture on tensile strength, and study the cracking mechanism by combining with the theory of dissipative structure. The results show that the fracture development of the silty mudstone shows a spiral dynamic growth pattern, and the degree of fracture development is greater in the heat process than in the wetting process.Hygrothermal alternation and decreasing fracture inclination degrade the tensile strength of silty mudstone, and the energy acceptance of the splitting process is weakened with the increasing number of alternations, with a decreasing proportion of elastic energy and an increasing proportion of dissipated energy. The fracture extension of the silty mudstone can be regarded as the process of dissipative structure gradual formation, in the process of hygrothermal alternation in the silty mudstone energy, material exchange mode is constantly changing, the internal structure is constantly adjusted to reach the critical state, the system mutation fissure emergence and development. The results of the study can provide some theoretical references for the safe protection of mudstone slopes.