To explore the washback of the HSK on students learning Chinese as a Second Language (CSL), the study surveyed 1,616 SCL students from 25 different mother tongue backgrounds and interviewed international students studying in China through questionnaire and interview. The following was found in this study: (a) The HSK influenced both the process and results of CSL learning, and the positive impact outweighed the negative impact. (b) Students' motivation and perception of the HSK were the key factors that influenced the level of HSK washback. (c) The HSK had different intensities of washback on students at different HSK levels, with the strong effect on students at the lower level and a weak effect on students at the higher level. Based on the findings, some implications and suggestions for learners, teachers and test designers are provided.