Modern Chinese Dictionary, as a medium-sized Chinese language reference book, plays an important role in Chinese language learning and researching. As it has a broad influence, the potential flaws in annotation would bring out negative impact on readers. Take the 7^th edition of Modern Chinese Dictionary for example. The writer finds out some mistakes in it through careful study. In annotation, there are mistakes such as “incorrect and inappropriate definitions, over-extended as well as under-extended denotation of the definitions, and missing as well as redundant senses of the entries, for every of which, a certain number of individual examples are included. The problems in annotation should especially draw attention of the lexicographers and the language learners. Pointing out and correcting the mistakes is obligatory both for upholding the authority of Modern Chinese Dictionary and for restoring the real sense of Chinese lexicon and the definitions of specific words. It is also of great realistic guiding significance for language learning and researching.