Abstract: This study adopted Mental Health Test (MHT) to investigate how the two factors of being left-behind and grade influence rural children's mental health. Subjects were 117 left-behind children in rural Anhui. The findings are that 1) significant difference is found in 3-score and 8-score standards respectively; 2) detection rate of interpersonal anxiety, impulsive tendency, aggressive tendency and loneliness in left-behind children is significantly higher than children staying with parents; 3) children staying with parents has higher loneliness than left-behind children; 4) there are significant differences of learning anxiety, interpersonal anxiety, fear tendency and physical symptoms among all grades of left-behind children, and stduents in Grade Seven have the highest anxiety and tendency; 5) female left-behind children have higher anverage score in all items except impulsive tendency. Some conclusions can be draw from the findings that dual-baseline standard has excellent practical effect, 3-score standard for the prevention and 8-score standard for clinical diagnosis, that left-behind children feel lonelier than children staying with parents, and that female left-behind children are more vulnerable to mental health than the male left-behind children.