Background <p>Chinese international students (CIS) form the biggest cohort in popular host countries such as the United States, Australia, and the United Kingdom, but research shows that their mental health is challenged by multifaceted stressors. Despite this, we are unaware of any previous systematic review that has synthesised both quantitative and qualitative findings on factors associated with their mental health across different countries, and no existing review has included studies done during or after the COVID-19 pandemic. This systematic review aims to answer the following questions: What are the factors associated with the mental health of CIS across different countries? Among identified factors which factors emerged during the COVID-19 pandemic, and which were exacerbated during the pandemic?</p> Methods <p>This review follows PRISMA guidelines. Six English and three Chinese databases were searched in November 2023: PsycINFO, MEDLINE, Embase, ERIC, Scopus, Web of Science, CNKI, Wanfang, and VIP. All types of empirical studies were eligible. Quality was assessed using the Mixed Methods Appraisal Tool (MMAT). Data were extracted and findings were narratively synthesised using a convergent approach.</p> Results <p>Thirty-nine English language papers and one Chinese language paper were included. The mental health of CIS is associated with various factors, including academic issues, parents and family, language proficiency, social support, discrimination, acculturative stress, the COVID-19 pandemic, and other factors. Among these, academic-related issues are their main concern, intertwined with family expectation and Confucian cultural values. Language plays a fundamental role in their daily life. During COVID-19, other than pandemic-related fear, there was an increase in experiences of discrimination and social isolation, associated with poorer mental health. Satisfaction with online learning is related to better mental health. Concerns about face, self-esteem, perfectionism, physical health, green space usage, and other factors were also reported.</p> Conclusions <p>The mental health of CIS is associated with various factors, and it worsened during the pandemic. Universities, and professionals in education and mental health could provide resources for students to enhance language abilities, academic skills, and social networks. CIS could be more prepared academically and mentally. Suggestions on future research directions were also provided.</p>