In the context of the emerging multizone circulating reactor (MZCR) operating with gas–solid phases, maintaining pressure balance is crucial for both reactor stability and achieving intended product quality. In this study, the method of moments, reactor model and pressure balance model are coupled to model and analyze an entire process flow for propylene (co)polymerization, which integrates a pre-polymerization tubular loop reactor (TLR) with a main polymerization MZCR. The modeling results unveil the relevance of pre-polymerization in the entire MZC process. Additionally, the influence of typical operating parameters on both the pressure stability and copolymer properties is investigated. To further visually identify the pressure-stable boundary of the MZCR, a method based on analyzing the pressure balance loop is proposed. The current study has illustrated the variation trends of pressure drops and product properties under typical operating conditions, identifying an operational range essential for reactor safety.