In order to effectively use the disintegrated carbonaceous mudstone in engineering practice, the disintegrated carbonaceous mudstone was modified with cement and fly ash. In this paper, the mechanical properties of the modified disintegrating carbonaceous mudstone are analyzed through the unconfined compressive strength tests of modified disintegrated carbonaceous mudstone with cement and fly ash combinations and different curing time, and the mechanism of modification was revealed by X-ray diffraction and scanning electron microscopy. The results show that when the disintegrated carbonaceous mudstone is modified with combination of 9% cement and 10% fly ash, its unconfined compressive strength reaches the maximum on 2.39 MPa, 2.68 MPa and 2.94 MPa at 7, 14 and 28 days, respectively. The X-ray diffraction (XRD) and scanning electron microscope (SEM) show that the pores inside the modified disintegrated carbonaceous mudstone are filled with hydration products with the increase of curing time, and the structure is gradually compact. The strength of modified disintegrated carbonaceous mudstone is enhanced due to the change of its microstructure.