Addressing the skill gap between labor market requirements and graduate readiness is crucial for the sustainable development of China’s vocational education system. This study investigated how outcome-based education (OBE) influences the attainment of graduate competence in China’s higher vocational education system, using the theory of Constructive Alignment (CA) as its foundation. The OBE model incorporates intended learning outcomes, project-based learning, and assessment strategies to ensure graduate competence aligns with professional sustainability practices. This study assessed the impact of intended learning outcomes, project-based learning, and assessment strategies on graduate competence attainment through surveys administered to 320 Cross-border E-commerce learners in April 2024, resulting in 301 usable responses. Data were analyzed using structural equation modeling (SEM) with SPSS 23.0 and AMOS 24.0. The results indicated that project-based learning and assessment strategies were directly and positively related to graduate competency attainment, while intended learning outcomes were indirectly associated with graduate competence through the mediating roles of project-based learning and assessment strategies. Assessment strategies had the most significant mediating effect, followed by project-based learning and the combined mediating effect. These findings advance the theoretical understanding of OBE and provide methods for promoting sustainability in vocational education. Beneficiaries include educators, policymakers, and accreditation bodies, who can use these insights to implement sustainable educational practices and ensure graduates contribute to sustainable development.