An automatic agent-adding device (100), used to add an agent to a surface of a workpiece. The automatic agent-adding device (100) comprises: a liquid storing container (10) used to contain the agent and connected with an air charging channel (110) and a liquid charging channel (111); and an air charging member (20) connected to the air charging channel (110). The air charging member (20) is used to charge compressed air into the liquid storing container (10) via the air charging channel (110), such that the agent flows out of the liquid storing container (10) and enters the liquid charging channel (111). An end portion of the liquid charging channel (111) away from the liquid storing container (10) is located above the workpiece.