Assignments are an important tool to evaluate learners’ learning effectiveness in online courses. Clarifying assignment design strategies is of great significance for promoting the quality construction of online education courses. This paper uses Bloom’s taxonomy framework revised by Anderson and Krathwohl (2001) as a reference to label the knowledge types and cognitive dimensions in the assignment context of eight courses. Combined with a literature review, a discipline–objective–schedule (DOS) threedimensional analysis framework based on the achievement of curriculum objectives, the design of chapter schedule, and the heterogeneity of disciplines is constructed to conduct an in-depth analysis of online course assignment design strategies. The research findings show that the online course assignment design strategy has an obvious curriculum objective orientation, follows the gradual learning rule, and presents typical disciplinary differences. The study finds that the current assignment design of online courses has three issues: first, a mismatch between assignment design and curriculum objectives; second, a lack of diversity in assignment formats; and third, insufficient comprehensiveness of some subject assignments. Based on the above discussions, corresponding suggestions are provided.