By employing four methods including questionnaire survey,test papers,classroom observation and interview,the authors conducted a theme-based CBI experiment in University of Shanghai for Science and Technology(USST).The study lasted for half a year.Before the study,the authors carried out a questionnaire survey about needs analysis of writing course for Chinese Science & Engineering Majors(SEMs)in order to know their English writing problems.According to the survey results and characteristics of theme-based CBI,teaching activities of College English writing component were designed.The effect of theme-based CBI on English writing proficiency is explored through analyzing the collected data with SPSS 19.0.