【Objective】 To explore the relationship of graduate students’ psychological stress and perceived stress with their mental health, and analyze the mediating effect of perceived stress. 【Methods】 We investigated 705 graduate students by Chinese College Student Mental Health Scale (CCSMHS), Chinese College Student Psychological Stress Scale (CCSPSS), and Perceived Stress Scale-10 (PSS). Correlation and structural equation model analysis was made. 【Results】 The graduate students’ psychological stress and perceived stress had significant correlation with their mental health. SEM analysis showed that perceived stress served as a partial mediation variable between psychological stress and mental health. Psychological stress had direct effects (0.216) for mental health and indirect effects (0.126) through perceived stress. 【Conclusion】 Graduate students’ psychological stress can influence their mental health directly, and can also reduce mental health level by increasing perceived stress. Perceived stress has partial mediating effect between psychological stress and mental health.