An automatic liquid supply planting device has a base, a planting holder mounted on the base, a liquid supply module, and a bottle. The liquid supply module is mounted on the base and has a liquid supply base mounted on the base and having a liquid guiding hole. The liquid supply bottle cap is detachably mounted on the liquid supply base and has a cap body detachably inserted into the liquid supply base, a base wall annularly formed on an inner side of the cap body and located at an end of the cap body, and a liquid outlet hole formed through the base wall and communicating with the liquid guiding hole. The bottle is detachably combined with the cap body and has an inner space communicating with the liquid outlet hole.
