Based on the stress process theory and life course theory, this paper studies the trajectory of mental health of the rural elderly by using the longitudinal data obtained from the survey “Well-being of Elderly in Anhui Province” from 2001 to 2018. The results show that age trajectory of mental health of the older people in rural areas follows a curvilinear pattern. With the increase of age, the life satisfaction of the older people increases at first and then decreases, while the depression increases. The cohort trajectory of life satisfaction follows an inverted U-shaped pattern,and the depression follows a U-shaped pattern. The cohort groups born earlier and later have the lower life satisfaction and the higher depression level, while the middle cohort groups born in the first half of 1930s have the highest level of life satisfaction and the lowest level of depression. Marriage and work stage have some influence on the mental health of the rural older people.The rural older people who are women, or with lower income or more negative life events have poorer mental health. The rural older people with better self-rated health, higher financial support or more emotional connection have better mental health.