In order to explore the change trend of mental health of left-behind children when time passes by,a total of 90 journal papers with MHT scale published from 2004 to 2017 are introduced for cross-temporal meta-analysis.The results of study show:(1)the learning anxiety and allergic tendency are positively correlated with the era,but other factors are negatively correlated with the era.14%to 23%of each factor variation can be explained by the era.(2)The anxiety to people,physical symptoms,panic tendency and impulsive tendency drops 0.06~0.73 standard difference averagely.The score of learning anxiety rose by 3.44,with explanation rate at 23%.(3)Compared with left-behind boys,left-behind girls are better improved in anxiety to people,panic tendency and impulsive tendency.(4)Compared to left-behind children in primary schools,the learning anxiety and allergic tendency of left-behind children in junior high schools is decreasing year by year.(5)The mental health of left-behind children in Central China and East China is improving faster than that of left-behind children in West China.As a whole,the learning anxiety of left-behind children is increasing gradually,but the overall mental health of left-behind children is improving in a step-by-step manner.