To investigate the fracture characteristics of silty mudstone under moisture-thermo-mechanical conditions， fracture evolution tests were carried out， and the fracture development of silty mudstone under single-factor cycles and multi-factor coupling cycles was obtained. Meanwhile， X-ray diffraction and scanning electron microscope were employed to examine the microstructural change of silty mudstone. By combining the correlation of macro and micro test results， the crack propagation mechanism of silty mudstone under moisture-thermo-mechanical conditions was revealed. The results show that the fracture development of silty mudstone under moisture-thermo-mechanical conditions generally exhibits a growth-gentle trend. Under single-factor cycles， humidity cycles （soaking-drying） are most likely to cause fracturing of silty mudstone， followed by temperature cycles （5~60 °C） and mechanical cycles （0~50 kPa）. Under multi-factor coupling cycles， their order to cause fracturing is moisture-thermo-mechanical cycles， moisture-thermo cycles， moisture-mechanical cycles， and thermo-mechanical cycles， which verifies the finding that humidity cycles are the dominant factor in causing fractures. After 15 moisture-thermo-mechanical cycles， the fracture rate can reach 0.92%， the number of fractures increases up to 30， the average fracture length extends to 60.58 mm， and the average fracture width is stable at about 0.47 mm. The gray correlation between the porosity and fracture rate is the largest， which is 0.813， indicating that the correlation between pore development and fracture expansion is the greatest in microstructure changes. Under moisture-thermo-mechanical conditions， humidity cycles cause the interlayer spacing changes of clay minerals， resulting in particle breakages and pores expansion to form microcracks. The temperature cycle produces differential thermal stress and water distribution in silty mudstone， which promotes the development of microcracks. The mechanical cycle increases the fracture tip stress and finally leads to a fracture network.