The invention discloses a preparation method of a small column sample used in loose rock experiment. The preparation method comprises following steps: 1, sampling, wherein a small column sample to be prepared is taken as the center so as to obtain a rock sample from a rock core via chiseling; 2, sample pretreatment, wherein the rock sample is immersed in liquid carbon dioxide, the temperature of the system is reduced to -80 DEG C or lower so as to freeze the rock sample by solid carbon dioxide and obtain a solid carbon dioxide frozen rock sample; 3, small column sample chiseling, wherein the small column sample is obtained via chiseling of the solid carbon dioxide frozen rock sample; and 4, small column sample treatment, the small column sample is subjected to finishing, is packaged, and is subjected to air drying so as to obtain a finished product. The preparation method can be used for obtaining small column samples at field fracture developing zones with permeability of 1000mD grade; problems of the prior art that preparation of samples with poor cementation degree, high weathering degree, and fracture development is impossible to realize, and only samples with permeability smaller than 15mD can be obtained are solved.