Existing respiratory gating devices are either contact-based or non-contact-based. Contact-based methods measure physical changes from respiratory movements through direct body contact, while non-contact methods do not. Two main issues arise: (1) Varying surface movements across different body regions (abdomen, chest, back, sides) complicate standardization; (2) Surface movement is not strictly correlated with respiratory gases, as significant gas exchange may occur with minimal surface movement at the end of inhalation or exhalation. To address these challenges, this paper presents a respiratory flow monitoring device and a respiratory drift limit compensation algorithm, providing accurate reflection of the patient’s respiratory condition.