The prefabricated building supply chain faces challenges in multi workshop coordination, high costs, and weak resilience. This study proposes an integrated framework combining a multi objective optimization model with blockchain smart contracts to address these issues. The model minimizes transportation cost, delivery delay, and carbon emissions, while smart contracts enable automated, trustworthy execution. Case study results show transportation cost reduced by 25.9%, on time delivery increased by 17.9%, carbon emissions cut by 28.8%, and the default rate dropped from 8.5% to 2.1%. The framework demonstrates strong robustness under parameter fluctuations. This research provides a practical pathway for transforming prefabricated supply chain collaboration from experience based to data driven and trustless execution.