The invention belongs to the technical field of porous carbon fibers, and particularly relates to porous carbon fibers with controllable porosity and pore structure and a preparation method of the porous carbon fibers. The preparation method comprises the steps that molded porous carbon fibers are immersed in a solution capable of reacting to generate calcium carbonate precipitation, the porous carbon fibers are taken out after the reaction is completed and dried, and the porous carbon fibers are obtained. According to the porous carbon fibers with the controllable porosity and pore structureand the preparation method of the porous carbon fibers, one or more liquid reactant is used for immersing a porous medium, an additional liquid reactant is added and enabled to be subjected to a chemical reaction in gap of the porous medium, and the porosity is changed in a mode of generating solid sediment, so that control and modification of the pore structure and porosity of the molded porouscarbon fibers are realized; and when the porous carbon fibers modified by the calcium carbonate precipitation are used as porous wicks of an evaporator in a loop heat pipe, the problems that the operation efficiency is reduced and even an operational failure occurs due to the fact that large pores in the porous carbon fibers enable steam generated during operation of the loop heat pipe to leak reversely to a liquid storage chamber can be effectively solved.