The invention provides a preparation method for endocyclic dicyclopentadiene and a device thereof. The method comprises the following steps: raw materials dicyclopentadiene enter a polymerization reactor to be heated to 20 DEG C to 45 DEG C to carry out polymerization reaction; the materials are forced to circulate in a polymerization process with the polymerization reaction time for 3 to 24 h; and the endocyclic dicyclopentadiene is obtained after the reaction is completed. A kettle body of the polymerization reactor is connected in series with a force circulation device; and the force circulation device comprises a force circulation pump and a honeycomb duct, and is connected with the kettle body through the honeycomb duct. In the polymerization reaction, a mode of forcing the materialsto circulate is adopted, the polymerization temperature in the polymerizer can be kept to be uniform, the materials slowly react, the polymerization reaction basically can not generate ring hanging type dicyclopentadiene under the reaction conditions, and the content of the endocyclic dicyclopentadiene in a prepared polymerization reaction product reaches more than 99 percent.