The invention relates to the field of catalytic materials for waste water treatment, and discloses a preparation method of a sisal hemp carbon fiber photocatalyst. The preparation method comprises the following steps: firstly, calcinating sisal hemp into porous carbon fiber with strong adsorption effect, and loading titanium dioxide nanoparticles and molybdenum disulfide quantum dots onto porous carbon by adopting a sol-gel method to obtain a tri-compounded porous carbon material. Through the photocatalyst, not only can the energy gap of titanium dioxide be reduced, but also the transfer efficiency of electrons can be enhanced, the visible light response range of the catalyst can be extended, and the modified titanium dioxide photocatalyst has response to visible light with wavelength of more than or equal to 460nm. According to the preparation method, the high-efficiency utilization of resources can be realized by fully utilizing natural sisal hemp, thus meeting green ecological concept. The preparation method of chemically modified sisal hemp carbon fiber photocatalyst is simple in technology, low in cost, and applicable to industrial production.