This paper presents a health monitoring system by incorporating the approach of user centered design (UCD) for enhancing system usability for the elderly. The system is designed for monitoring cardiovascular diseases (CVD) related physiological signals including electrocardiogram (ECG), pulse wave (PW) and body weight (BW). Ease of use and non-obtrusiveness are two key requirements for design criteria. Our health monitoring system is designed on three levels: personal medical device layer, mobile application layer and remote central service layer. A chair-based apparatus was built for physiological signal acquisition and a mobile application was developed for data delivery and health management. Finally, usability evaluation was conducted and the system efficiency was quantitatively analyzed by system usability scale (SUS). The results demonstrate that the performance of the system is acceptable for the elderly and the UCD principle is helpful for health system design.