Given the far-reaching impact of K-12 online education on China's educational services, the study explores the relationship between achievement goal orientation, online learning task value, motivational regulation strategies and academic procrastination using the questionnaire approach with 880 junior high school students who are studying online courses through various online platforms. Results indicated that (1) mastery-approach orientation was related negatively, while performance-avoidance orientation was related positively to academic procrastination. Correlation between mastery-avoidance orientation, performance-approach orientation and academic procrastination failed to reach significance. (2) Mediation analysis verified task value as a partial mediator of the effect of mastery-approach on academic procrastination, and its suppressing effect of the direct effect of mastery-avoidance and performance-approach orientations on academic procrastination. (3) The analysis also validated motivational regulation as a partial mediator of the effect of mastery-approach on academic procrastination, and its suppressing effect of mastery-avoidance and performance-approach on academic procrastination. (4) Task value and motivational regulation also play a chain mediating role between mastery-approach and academic procrastination, while their chain mediating effects of mastery-avoidance and performance-approach on academic procrastination turn out to be suppressing effect. Recommendations were made based on the analysis to improve the students' online learning efficiency.