Abstract: In the process of new urbanization， Chinas left-behind children are in a state of lacking regulation or supervision， thus facing great social risks. A multidimensional risk index was constructed based on 8 dimensions and 27 indicators such as accident risk， two-way crime risk， psychological sub-health risk， physical health risk， behavior anomie risk， communication failure risk， education failure risk and adverse environment risk. The weights of such indexes were calculated by using the expert scoring method， and each left-behind childs comprehensive multidimensional risk index was obtained by using the AHP method. The integrated risk value was divided into five levels and five warning and intervention mechanisms were established accordingly so as to alleviate or reduce social risks the left-behind children face and strengthen their protection and guidance.

Key words: left-behind children, multidimensional risk index, early warning, graded intervention