The invention relates to a cyclic oligosaccharide based oil solidifying agent and a preparation method thereof, and belongs to the field of petroleum industry. The oil solidifying agent is used to treat oil overflowing in seas or rivers and oil leakage of pipelines on land. The oil solidifying agent is composed of the following components in percentage by weight: 18.95 to 23.06% of beta-cyclodextrin, 6.10 to 6.68% of dicarboxylic anhydride, 17.78 to 18.27% of aliphatic acyl chloride, 5.69 to 6.01% of NaOH or KOH, and 47.38 to 50.08% of strong acid salts of iron or aluminum. The oil solidifying agent is synthesized in an organic solvent and a mixed solution of an organic solvent and weak alkaline water. The oil solidifying agent is used to oil overflowing in seas or rivers and oil leakage of pipelines on land, and has the advantages of simplified synthesis steps, improved preparation efficiency, and good treatment effect.