This paper investigated a large number of errors found in the topic-based writings of Chinese EFL learners, especially provided an analysis on frequent errors, to find useful pedagogical implications for English grammar teaching and writing instruction in Chinese EFL setting. Students' topic-based writings were examined by the author. The findings suggest that misuse of tense and verb form was the most frequent error in Chinese students' writings. Others include those in spelling, use of particular words and phrases, Chinese-English expression, singular and plural form of nouns, parts of speech, non-finite verbs, run-on sentences, pronouns and so on. Teachers should pay due attention to all of the errors, especially those frequent ones, and try to find out what leads to those errors, thus, they may give their students effective grammar and writing instructions to help them with English learning.