The invention discloses a preparation method for activated carbon fibers with a photocatalysis function. The activated carbon fibers for immobilizing graphite phase carbon nitride are prepared by an electrochemical deposition method by taking activated carbon fibers, dicyanodiamine, N,N-dimethylformamide and the like as main raw materials. The activated carbon fibers have an adsorption function and the photocatalysis function. Under a condition of darkness or insufficient light, pollutants can be purified under the adsorption function of the activated carbon fibers; under a condition of sufficient light, the pollutants can be purified under the adsorption function and the photocatalysis function; in-situ regeneration of the adsorption function of the activated carbon fibers can be realized; labor, resource and financial consumption of a regeneration process is greatly reduced. Successful research on the activated carbon fibers has an important significance for relieving of insufficience of activated carbon fiber supply in China.