Abstract: Using MMHI-60, SSSCLB and ALSEC, this article presents a survey of 2,219 rural children left behind. The results suggest that: (a) in general, the mental health of children left behind is worrying, with significant variation among different levels of sense of security ; (b) life events are in positive correlation to mental health, and sense of security is significantly negative to mental health; (c)sense of security plays a significant regulatory role in life events and mental health; (d) life events can directly predict mental health, with sense of security playing partial mediating effect on mental health in life events; (e)the left-behind situation is an important factor affecting the mental health, while sense of security plays a complete intermediary role between the left-behind situation and mental health of children left behind in China.