The diagnostic test for Chinese character learning provides students with an accurate report on their character acquisition skills, thereby enhancing targeted instruction. This study constructs a cognitive diagnostic Q-matrix for Chinese characters based on the Chinese Proficiency Grading Standards for International Chinese Language Education, focusing on the learning skills and cognitive processes of Chinese characters as key assessment areas. A cognitive diagnostic assessment was conducted on 198 Chinese as a second language (CSL) learners in China. The study provides detailed feedback for group and individual levels, supporting personalized instruction. The diagnostic results indicate that students from both grades exhibit better mastery of strokes and structure compared with components and holistic characters, and their mastery of stroke quantity surpasses that of stroke order. Second-year CSL learners outperform first-year CSL learners in all cognitive skills, with the most significant improvement observed in stroke order and holistic character skills. The findings of this study can offer guidance and implications to Chinese character instruction.