The complexity of the structure and operating process of the large-scale petrochemical equipment makes it difficult to realize effective health management. In this article, a natural gas dehydration process digital twin (DT) is proposed for condition evaluation. The framework and detailed DT models are introduced. The geometric, process, behavioral, and rule models in DT map physical entities geometric information, working process, control process, and hidden condition evolution process, respectively. A triethylene glycol dehydration DT application system is developed and the overall reality-virtual mapping process of DT for equipment condition evaluation is demonstrated. The ability of the DT to represent the petrochemical processes is verified with real monitoring data. The condition evaluation ability of the DT application system is validated by failure event and typical process parameters. The methodology proposed in this article can be applied to petrochemical fields to improve the safety of the operational process.