The invention discloses a preparing method of high-water-absorption antibacterial acrylic fiber, and belongs to the field of acrylic fiber preparation. The provided preparing method includes the steps that a culture medium is inoculated with streptomycete, modified hyphae are obtained through screening and modifying, then the modified hyphae are mixed with starch and the like to prepare a modified matrix, the modified matrix is mixed with polyacrylonitrile and formaldehyde, the pH value is adjusted, N,N-methylene bisacrylamide is used as initiator for carrying out graft modification reaction, air is exhausted, the product is stirred and cooled to the room temperature, and then the high-water-absorption antibacterial acrylic fiber is obtained through discharging, drying, curling, cutting and packaging. The method is unique and novel, as the microorganism is added to serve as antibiont, starch is modified for graft modification, the prepared acrylic fiber has high water absorption and antibacterial performance, and own defects of the acrylic fiber are overcome; the preparing process is simple and easy to implement, the raw materials are simple and easy to obtain, cost is low, and the acrylic fiber is suitable for large-scale application and popularization.