The invention relates to the technical field of municipal gardening, in particular to a municipal gardening rainwater collecting device. The device comprises a rain water collecting box which is arranged on a tree trunk and used for collecting rainwater, a drainage port formed in the rainwater collecting box, a drainage pipe which is communicated with the drainage port and used for irrigating trees, a flow gate which is slidably connected with the inner wall of the rainwater collecting box, a driving member used for driving the flow gate to slide to control the opening and closing of the drainage port, a soil humidity sensor embedded in the soil in the periphery of the tree trunk and a controller. The soil humidity sensor is electrically connected with the signal input end of the controller, and the driving member is electrically connected with the signal output end of the controller. By means of the device, automatic adjustment of the water using amount for irrigating the trees is achieved to facilitate the growth of the trees.