The oligomerization of endo-dicyclopentadiene (endo-DCPD) in a continuous-flow reactor at elevated pressure was studied to produce tricyclopentadiene (TCPD) that was the precursor of high-energy-density fuel. The composition of the products and possible reaction pathway were analyzed, and the effects of reaction conditions were evaluated. Compared with the batchwise reaction at atmospheric pressure, the continuous-flow process could significantly enhance the reaction, increase the exo/endo ratio of TCPD, and produce a new product exo-DCPD. The exo/endo ratio was linearly dependent on the selectivity of exo-DCPD. A high pressure of above 1.2 MPa was necessary to facilitate the reaction. The conversion of endo-DCPD increased with the increase of temperature, while the yield of TCPD reached the highest value at 160°C. But the exo/endo ratio decreased with the increase of temperature. The conversion of DCPD and the yield of TCPD increased when the residence time was increased, but the reaction rate decreased. A short residence time was favorable, because it led to a high exo/endo ratio for TCPD. The effect of feed concentration was limited. Under the optimal condition, the conversion of endo-DCPD was 82.2% and the yield of TCPD was 41.7%.