The Industrial Internet of Things (IIoT) is crucial to contemporary industrial ecosystems because it increases efficiency and innovation. However, its swift growth also poses some serious security challenges, especially concerning the management of identities. This research paper introduces a new approach to strengthen IIoT security by using a Decentralised Identity Management System with Blockchain-based MFA. This study suggests an architecture for IIoT digital identity management that involves a private Blockchain network along with smart contracts and different types of MFA to build up one secure, reliable, and tamper-proof system. The approach is evaluated using a wide simulation environment, copying real-world scenarios of IIoT and attack vectors. Key performance metrics used in the analysis of the system include Authentication Success Rate, Incident Detection Rate, System Resilience Score, and Average Response Time under different circumstances, such as normal operations and attempts to break security. Results show great efficacy in authenticating legitimate access, high resistance against common cyber-attacks such as brute force and identity spoofing, and the best combination of security versus performance. This research adds significant value to the IIoT security area because it offers a holistic approach that can help fill in vital gaps concerning risk points within decentralised systems and, hence, lay the groundwork for safer and more productive industrial operations with digitalisation processes.