Synthesis of 5-vinyl-2-norbornene based on the Diels-Alder reactions of cyclopentadiene (CPD) generated from dicyclopentadiene (DCPD) and 1,3-Butadiene (BD) have been investigated in a continuous tube reactor under high temperature and high pressure. The experimental results show that the concentration of main product 5-vinyl-2-norbornene (VNB) increases with the increasing of reaction time at low reaction temperature. The elevated temperature greatly promotes the synthesis rate of both product VNB and its isomer cis-3a,4,7,7a-tetrahydroindene (THI) and tricyclopentadiene, resulting in a mountain-shaped curve of VNB concentration versus the reaction time. Particularly, it has been confirmed that the trimer (4,4a,4b,5,8,8a,9,9a-octahydro-1H-1,4-methanofluorene should be prepared by direct reaction of BD with DCPD rather than by the reaction of CPD with VNB or THI. This comprehensive study can lay a solid foundation for the process optimization of VNB synthesis.