The utility model discloses an automatic watering device for bonsai. The automatic watering device comprises a controller, a humidity sensing mechanism for sensing bonsai soil humidity, a watering mechanism, a faucet, a first electromagnetic valve, a first water pipe and a water pump, wherein the humidity sensing mechanism comprises N humidity sensors which are connected with the controller; the watering mechanism comprises a suspension mechanism, a pond fixedly connected with the suspension mechanism and N watering units, the pond includes an upper water storage pond and a lower watering pond, the water storage pond is fixedly connected with the watering pond, the faucet extends into the water storage pond, each watering unit comprises a second water pipe, a second electromagnetic valve for controlling the water connection of the second water pipe and a sprinkler, the upper portion of the second water pipe is located in the water storage pond, the lower portion of the second water pipe is located in the watering pond, the bottom of the second water pipe is connected with the sprinkler, and the second electromagnetic valve is connected with the controller. The automatic watering device has the advantages that the device can water a large amount of bonsai at the same time and is low in cost, small in floor space and high in watering efficiency.