Purpose To reduce the potential risk during radiotherapy treatment of patients with head and neck tumors, we improved upon the design of an existing immobilization device by adding a feature to improve patient safety during emergency releases, and we verified its clinical application. Method We designed an improved automatic unlocking baseplate (AUB), and conducted a dosimetry comparison with Solo Align Full Body System (SAFBS, Klarity, China). The dosimetry comparison included dose-attenuation measurements and results from human simulation. We selected four points for measurement to allow comparison between the SAFBS and our AUB. A simulated human body model was used for CT scanning, whereby the target area and structure and simulated radiotherapy plan were conducted according to the American Academy of Pain Medicine Task Group-119 report (TG-119), whereby the dose differences were compared. The purpose of the clinical test was to verify the reliability of the AUB system in practical clinical applications. The application tests were conducted in CT simulation (CT-sim) and treatment rooms. The test included assessments of the stability of the system and the reliability of our device. Results The dose-attenuation measurements of the two baseplates were as follows: The transmission values with our unlocking system were 0.10% higher at the first point and 0.67% lower at the third. The same dose was obtained at points 2 and 4. In the simulation study, the PTV of the AUB was lower than that of the SAFBS, including 0.39% lower D-99 and 0.18% lower D-90. Among the organ-at-risk doses, the average dose of the AUB in the spinal cord was 0.6% higher than that of the SAFBS, and the average dose in the left and right parotid glands was more than 1.4% lower than that of SAFBS. The clinical test results were applied in treatment room and a CT-sim room, which show a 100% success rate after being unlocked more than 5000 times. Conclusion The AUB designed for head and neck patients had good functional versatility, the dose distribution met the requirements, and the automatic unlocking function was demonstrated to be stable and reliable.