Gamification mechanisms have been increasingly integrated into educational environments to enhance learner's engagement and improve the effectiveness of online courses. However, the precise effects of gamification on learner's engagement, including the factors that influence this behavior, remain under-explored. This study addresses this gap by examining the relationships between learner's interactions with three gamification strategies (i.e. contextualized content, constructive achievement, and social expression) and their intention to engage in learning activities. Using a sample of 463 learners from the Android Programming Technology course on a massive open online course (MOOC) platform in China, data was collected through a questionnaire survey and analyzed by a structural equation model. Using self-determination theory and the theory of rational action as the theoretical foundation, we empirically tested the proposed model and hypotheses through a structural equation model. The results indicate that gamification design strategies significantly impact learners' autonomy ([beta] = 0.305, p < 0.001), competence ([beta] = 0.312, p < 0.001), and relatedness ([beta] = 0.295, p < 0.001), which are essential for fulfilling psychological needs. Furthermore, perceived enjoyment positively influences perceived usefulness ([beta] = 0.339, p < 0.001) and perceived behavioral control ([beta] = 0.645, p < 0.001), which jointly have a significant effect on learners' engagement intentions. Among the strategies, contextualized content had the strongest impact on perceived enjoyment ([beta] = 0.459, p < 0.001). These findings provide valuable insights for the design of gamified learning environments and contribute to the broader understanding of gamification's role in education.