An automatic positioning method and an automatic control device are provided. The automatic control device includes a processing unit, a memory unit, and a camera unit to automatically control a robotic arm. When the processing unit executes a positioning procedure, the camera unit obtains a first image of the robotic arm. The processing unit analyzes the first image to establish a three-dimensional working environment model and obtains first spatial positioning data. The processing unit controls the robotic arm to move a plurality of times to sequentially obtain a plurality of second images of the robotic arm by the camera unit and analyzes the second images and encoder information of the robotic arm to obtain second spatial positioning data. The processing unit determines whether an error parameter between the first spatial positioning data and the second spatial positioning data is less than a specification value to end the positioning procedure.