Rainwater collecting and utilizing device for roof greening

The invention relates to a rainwater collecting and utilizing device for roof greening. The rainwater collecting and utilizing device comprises a planting layer, a water supplementing unit and a drainage unit which are arranged in a planting container from top to bottom, the water supplementing unit comprises a rainwater collecting pool and a water supplementing channel, and the rainwater collecting pool and the water supplementing channel are communicated with each other; and the drainage unit comprises a ceramsite layer and a drainage filtering layer, a drainage pipe is vertically arranged between the drainage filtering layer and the bottom of the rainwater collecting pool, a moisture absorption cotton layer is arranged in the drainage pipe, and an overflow port is formed at the position, at the joint of the rainwater collecting pool and the water supplementing channel, of the side wall of the planting container. The rainwater collecting pool is connected with the drainage pipe, thedrainage filtering layer