Herein, we develop an approach to achieve performance‐advantaged polydicyclopentadiene (PDCPD) via sequential ring‐opening metathesis polymerization (ROMP) and radical reactions. Mixing dicyclopentadiene (DCPD), Grubbs' catalyst and radical initiator in one pot, then polymerizing firstly at low temperature by ROMP and initiating radical reactions at elevated temperature. Due to our strategy, the crosslink density of PDCPD increases, leading to outstanding performance. For instance, the glass transition temperature of ROMP prepared PDCPD is ca. 155–175 °C; whereas, the Tgs of PDCPD prepared by this strategy can be increased to 191 °C, and can be further enhanced to 216 °C after polymerization at 250 °C. We believe this can help researchers design and synthesize high performance ROMP‐derived polymers and apply PDCPD in harsh conditions.This article is protected by copyright. All rights reserved.