Under the "Double First-Class" initiative, the training of part-time engineering doctoral candidates aims to cultivate leading engineering and technical talents capable of solving complex engineering problems, promoting technological innovation, and organizing research and development. However, the current training process still faces systematic challenges, including the prominent contradiction between work and study, insufficient industry-university collaboration, the disconnect between dissertation topics and industry needs, and inefficient translation of research outcomes into practice, all of which hinder the achievement of the above goals. To address these issues, this study systematically diagnoses the key problems in the existing training model through specialized research and constructs a targeted and actionable "four-in-one" collaborative training system. This system consists of four interrelated core mechanisms: first, a work-study coordination mechanism designed to precisely alleviate time conflicts between work and study; second, a dual-supervisor appointment and dissertation planning and demonstration mechanism to strengthen the collaborative effectiveness of university and industry supervisors throughout the topic selection and guidance process; third, an integration mechanism for dissertation topics and project carriers, promoting the deep integration of dissertations with real industry projects; fourth, a mechanism for research outcome implementation and deep industry-university collaboration, facilitating the efficient transformation of research findings into practical productivity. Relying on these mechanisms, the training of part-time engineering doctoral candidates can achieve three major shifts: from an academically oriented approach to an engineering-oriented one, from single-institution management by universities to dual-entity collaborative education between universities and enterprises, and from short-term cooperative projects to long-term collaborative alliances. The study clarifies the core challenges in the training model for part-time engineering doctoral candidates. The constructed "four-in-one" collaborative training system provides a feasible pathway for the synergistic interaction of multiple mechanisms and enriches the practical framework for industry-university collaborative training under the "Double First-Class" initiative.