Background: The introduction of Small Private Online Courses (SPOCs) in English as a Foreign Language (EFL) instruction at Higher Vocational Colleges (HVCs) signifies a shift in education. Understanding the factors that affect deep learning in this SPOC context is crucial for improving educational outcomes. Objectives: By employing grounded theory, we seek to explore the key factors that shape deep learning experiences for students in SPOC learning environments at HVCs and clarify the interrelationships among these influencing factors. Methods: Semi-structured interviews were conducted with 18 EFL students and 4 teachers and NVivo 11 software was utilised to aid in the qualitative analysis of the collected data. Through a rigorous three-tier coding analysis, an "environment-person-mediation-behaviour" (EPMB) model was constructed, aiming to clarify the mechanisms that influence deep learning among EFL students in HVCs. Results: Our findings reveal that intrinsic motivation and cognitive abilities are crucial for deep learning among EFL students in HVCs. Blended learning settings, English curriculum satisfaction, and English teachers' teaching methods serve as situational influencing factors. These factors are interconnected, mediating positive or negative effects on deep learning through various intermediaries like continuity, attraction, guidance, motivation, and regulation. Implications: The findings offer pedagogical insights for HVC stakeholders, enabling them to enhance students' deep learning experiences.