This paper examines the frequency distribution and functions of ‘so’ and ‘OK’ in Chinese pre-service teachers’ and native teachers’ talks and explores the reasons why Chinese pre-service teachers overuse ‘so’ and ‘OK’. Based on a Chinese pre-service teachers’ corpus collected by the researcher and a pedagogical sub-corpus from Michigan Corpus of Academic Spoken English (MICASE), the frequency of ‘so’ and ‘OK’ in both corpora was examined through quantitative analysis and results showed that Chinese pre-service teachers use ‘so’ and ‘OK’ more frequently than native teachers. Statistical analysis with IBM SPSS indicated a great discrepancy between the two corpora, suggesting there is a spectacular degree of overusing ‘so’ and ‘OK’ by Chinese pre-service teachers relative to native teachers. Qualitatively, the functions of ‘so’ and ‘OK’ in both corpora were examined and results showed that although ‘so’ and ‘OK’ were used to achieve the same main functions in both corpora, Chinese pre- service teachers and native teachers have different perceptions of the primary sub-function of ‘so’ and ‘OK’ and Chinese pre-service teachers use ‘so’ and ‘OK’ improperly in some cases. Besides, qualitative analysis of interview answers reflected the essential impact that high school and college teachers have on their students’ understanding and use of discourse markers. The identification of these problems in Chinese pre-service teachers’ use of ‘so’ and ‘OK’ points to the great value of more focused discourse marker knowledge input through the process of teacher education and teacher training.