This study designed a system for evaluating personal stress by assessing activities of autonomic nervous system (ANS) using heart rate variability (HRV) analysis through Photoplethysmography (PPG) signal. To investigate the performance of stress relaxation, this study also designed an environment with personal preferences. The environment included visional, audio and olfactory elements. Five healthy college students were invited to five days stress task study. The personal preferences of environment were set before experimental procedure. The subjects were required to fill the State-Trait Anxiety Inventory (STAI), and PPG signal was acquired by the developed system during experimental procedure. The experimental procedure was composed with a sequence of initial rest for baseline, relaxation environment after rest, stress task and relaxation environment after stress task. Results indicated that a decrease in STAI and LF/HF was obtained during relaxation environment, whereas increase in STAI and LF/HF was obtained during stress task. These results suggested that an environment with personal preferences may improve helpfully for stress relaxation.