The sizes of a newly-developed non-invasive, cuffless blood pressure sensor are successfully optimized for maximizing its output signal quality. The optimization is conducted via establishing a coupled solid–fluid-electric model and considering varied mis-positionings. The non-invasive, cuffless blood pressure sensor consists of a gel-capsule and a strain sensor in a number of parallel electrodes. Towards sensing blood pressure, the BP sensor is designed to sense the vibration of radial artery by converting the deformation of the sensor electrodes to electrical signals. In practical uses, it is inevitable that the sensor is not placed right on the location where maximum vibration of the artery occurs, thus undermining the signal quality of the sensor output signals for accurate BP estimates. This study is dedicated to optimize the sizes of sensor electrodes with a required level of robustness to be able to obtain quality signals with presence of reasonable mis-positionings. The optimization is made possible by first establishing a coupled fluid-mechanics-electric model to predict sensor output due to dynamic artery dilations, and then the sizes of sensor electrodes are successfully optimized for maximum sensor outputs with consideration of reasonable mis-positionings. The range of sensor mis-positions considered is between −5 and +5 mm to cover all possible users in different heights, weights, ages, genders, etc. The optimal electrode length of the sensor is found to be 7 mm, while the accuracy of the predicted pressure levels are within ±7 mmHg, which conforms to the required accuracy of ±8 mmHg by The Association for the Advancement of Medical Instrumentation (AAMI).