The Chinese Proficiency Test or "Hanyu Shuiping Kaoshi" (HSK) significantly influences International Chinese Language Education (ICLE). The washback effect of the HSK has received less attention in earlier research studies. This study applied a mixed-methods research design to examine the HSK washback effect on ICLE in relation to value, intensity, length, specificity, and intentionality. It involves questionnaires, classroom observations, and interviews with international Chinese language teachers and international students as research subjects. The study reveals that HSK has a strong positive effect in terms of value and intensity. The effects occur both before and after the test for some time. The specificity of the washback effects is reflected in teachers' teaching contents, methods, and attitudes, as well as students' learning contents, methods, and attitudes; and in terms of intentionality. The design of HSK has been partially executed, but it produced unexpected consequences. To optimize the positive washback effects of HSK, this study offers practical recommendations for international Chinese language teaching and learning.