The invention relates to a preparation method of large-sized polyacrylamide cryogel and belongs to the technical field of cryogel preparation. According to the preparation method, buckwheat starch is modified for preparation of granular buckwheat starch, the granular buckwheat starch expands in volume after combined with water and is taken as a polymerization cryogel matrix skeleton, then polyacrylamide cryogel is prepared through polymerization, and a starch skeleton is hydrolyzed at 37 DEG C to form homogeneous pores due to uniform size of ultrafine buckwheat particles. The diameter of the large-sized polyacrylamide cryogel prepared with the method is 145-200 mm, the thickness is 22-23 mm, the size is increased by 15%-20% compared with like cryogel media, and the porosity of the cryogel medium can reach 81%-82%; the cryogel is prepared from starch in a recycling manner, so that resources are saved, and the method is environment-friendly and pollution-free.