The invention discloses a micromolecular cationic surfactant type anti-swelling agent. The anti-swelling agent is generated by reacting at least one fatty primary alcohol with a carbon number of 4-9,dimethylamine and benzyl chloride. A preparation method for the anti-swelling agent comprises the following successive steps: subjecting fatty alcohol and dry hydrogen bromide to a reaction to obtainan intermediate product, namely brominated alkane; then reacting the intermediate product brominated alkane with dimethylamine to obtain another intermediate product, namely dimethyl alkylamine; and finally, reacting dimethyl alkylamine with benzyl chloride to obtain an anti-swelling agent solid. The micromolecular cationic surfactant type anti-swelling agent is small in dosage, and aqueous solution with a concentration of 0.3 wt.% prepared from the anti-swelling agent can show good anti-swelling performance; and the micromolecular cationic surfactant type anti-swelling agent is high in anti-swelling efficiency and stability, has long-acting anti-swelling performance, is good in compatibility with fracturing fluids, and is safe and environment-friendly.