An automatic radiopharmaceuticals filling machine mainly comprises a main unit with an activation mechanism to perform three-dimensional reciprocal movement. The activation mechanism has a lateral slider that can be activated to move reciprocally along lateral X-axis. On the lateral slider, there is a vertical slider that can extend perpendicularly and move reciprocally along lateral Y-axis. An injection needle is located on the vertical slider and can be activated to move reciprocally along Z-axis perpendicular to the lateral slider. A syringe rack is located in the moving range of the injection needle to accommodate a plural number of syringes, on each of which there is an injection hole. A drug pump has an inlet and an outlet. The inlet connects to a high-dose radiopharmaceuticals drug bottle. The outlet connects to the injection needle. The drug pump withdraws the radiopharmaceuticals from the drug bottle to the injection needle and allows the front end of the injection needle activated to go through the injection hole into the syringe and fill the radiopharmaceuticals into the syringe.