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. What can we learn from the washback of the HSK?To explore the impact 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. For language learning, first, learning goals need to be clarified. Second, the HSK needs to be reasonably understood. Third, treat the test results need to be correctly. For HSK development, first, test developers need to reasonably design the difficulty gap between different HSK levels and balance the difficulty between different question types of the same level. Second, more HSK levels should be developed. Future research can focus on the personal background of learners and explore the impacts of factors such as gender, mother tongue and family on washback. At the same time, more attention should be given to social policies and administrators to expand the washback of the HSK.