Self-efficacy is an essential part of motivation that leads to the engagement in individual learning process. This study focuses on exploring the levels and sources of self-efficacy of foreign language learners who are in different learning stages. 518 students, as a sample of this study, were asked to fill in the questionnaire before it was analyzed by One-way ANOVA and t-test. The result shows the fluctuation of levels of self-efficacy. In terms of ranks of sources of self-efficacy, vicarious experience, mastery experience, emotional states, and social persuasion are the most influential sources respectively for positive self-efficacy with the increasing influential due to increasing years of learning; however, for negative self-efficacy, mastery experience was the highest rank of sources of self-efficacy followed by emotional states, vicarious experience, and social persuasion with the inclining influential upon years of learning. The results of this study will give language teachers greater ability to provide supporting facilities, activities, and materials more suitably at each stage of the language learning process.