A novel hybrid simulation approach is developed, which combines the advantages of deterministic and stochastic modeling of complex polymerization networks. The fast deterministic simulation solves the heat and pressure balances and generates position‐dependent event frequency profiles. The detailed stochastic simulation is used as add‐on and offers a deep insight into the polymeric microstructure of each macromolecule. Our hybrid simulation approach is applied to high‐pressure ethylene polymerization in industrial tubular and continuous autoclave reactors with peroxide initiation. But in general, the presented approach can be used for all types of polymerization reactions in ideal and non‐ideal reactors of any kind.