Abstract: Mudstone can soften and break down in contact with water. This behaviour is frequently encountered in mudstone roadbed engineering of open pit mines. It is highly important to improve the mechanical properties of mudstone. By using the X-ray diffractometer, three-dimensional laser topography measurement instrument, scanning electron microscope, Fourier transform infrared spectrometer, static water contact angle tests and mechanical experiments, the mudstone was characterized to investigate its change rules of composition, topography, contact angle, swelling ratio and sheer strength, respectively. More attention was paid to the micro-mechanism of organic, inorganic and double modification. The results show that the size of cracks increases with the increasing soaking time of mudstone, and it disintegrates in water 10 minutes later, however the mudstone does not disintegrate in water 2 days later after organic and double modification except for that modified by inorganic materials. The contact angle of water on the surface of mudstone is 2.6°; after organic and double modification, it increases to 116.3° and 119.4°, respectively; however it is only 4.5° for the mudstone modified by inorganic materials. After organic, inorganic and double modification, the swelling ratio of mudstone decreases from 16.7% to 11.2%, 4.2% and 2.4%, respectively. The sheer strength of mudstone decreases with the increasing water content before modification. After modification, both cohesion and internal friction angle increase with the increasing water content, and then decrease with the increasing water content. After double modification, the mechanical strength of mudstone with water content of 25% is optimum. Hydrophobic film forms in the surface of mudstone grains in the process of organic modification, however the mechanical strength of mudstone is enhanced slightly. The pores are filled by three-dimensional net gel texture in the process of inorganic modification. The cementation condition between grains of mudstone is improved by inorganic silicate materials, and the mechanical