This research attempts to discuss the validity of introducing the evaluation of students' critical thinking skills (CTS) into the assessment system of college English writing through an empirical study. In this paper, 30 College English Test Band 4 (CET-4) writing samples were collected and analyzed. Students' CTS and the final scores of collected writing samples were respectively regarded as two independent variables to make a correlation analysis through Pearson Correlation of SPSS17.0 software. In addition, Excel was also used as an instrument to analyze the research results. The findings suggest that the two variables are significantly and positively correlated with each other, that is, students' CTS greatly influence their English writing proficiency. Thus, it is quite necessary to cultivate students' CTS to improve their English writing competence.