The invention belongs to the field of inorganic water treatment agents, and in particular relates to an inorganic mineral water treatment agent and a preparation method thereof. The water treatment agent is prepared from 50-60 parts of natural zeolite, 25-30 parts of red vesuvianite, 8-15 parts of natural fibers, 3-4 parts of ferrite and 1-2 parts of H2O2 water solution with the mass concentration of 35%; the preparation method comprises the following steps: mixing the natural zeolite with the vesuvianite, performing treatment of crushing, washing with acid, radiation in infrared light and the like, further mixing the natural fibers with a mixture of the zeolite and the vesuvianite in vacuum, adding a soluble ferrite solution, later adding the H2O2 water solution, stirring, drying, calcining at high temperature, cooling and drying, thereby obtaining the inorganic water treatment agent. The water treatment agent is relatively large in adsorption space and adsorption capacity, and can solve the problems that a conventional water treatment agent is poor in effect in treating sewage with complex components, can pollute the environment and the like. The water treatment agent provided by the invention is easy to regenerate, is free of secondary pollution, and can be widely applied to purification treatment on the sewage.