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Introduction Invasive arterial blood pressure monitoring is critical for perioperative and critically ill patients, yet traditional radial artery cannulation near the wrist joint is prone to catheter dysfunction (eg, kinking, occlusion) due to positional changes, compromising accuracy and patient safety. This trial hypothesises that modifying the cannulation site to 1.5–2.5 cm proximal to the radial styloid process may enhance catheter stability.Methods and analysis This is a prospective, parallel-group, randomised, controlled, analyst-blinded trial. A total of 486 participants (243 per group) will be enrolled at the Sixth Affiliated Hospital, Sun Yat-sen University. Eligible patients (18–75 years, American Society of Anesthesiologists physical status I–III, requiring elective surgery with radial artery cannulation) will be randomised 1:1 to the modified group (1.5–2.5 cm proximal to the radial styloid process) or the conventional group (traditional site). The primary outcome is the incidence of arterial catheter dysfunction (defined by criteria such as blood sampling difficulty, position-dependent waveform or improved waveform post-square wave test). Secondary outcomes include frequency of catheter dysfunction, damping abnormality rate, first-puncture success rate, number of arterial punctures, arterial cannulation time, complication incidence and blood pressure measurement differences.Ethics and dissemination This study protocol (V.4.0) was approved by the Ethics Committee of the Sixth Affiliated Hospital of Sun Yat-sen University in Guangzhou, China on 2 September 2025. The first participant was recruited on 15 September 2025, with an estimated completion date of 31 December 2025. Informed consent will be obtained from all participants. Findings will be published in peer-reviewed journals.Trial registration number NCT06566456.