Pilots are required to have the ability to evaluate their own physical and psychological status to operate high performance aircrafts effectively. Existing studies have lacked consideration of applying bio signal of pilots in real time flight situation. The purpose of this study is to develop a wearable bio signal monitoring system that can measure the condition of pilots under an extreme flight environment to ensure flight safety. The wearable bio signal monitoring system consists of an algorithm for evaluating pilots' physiological stability, algorithms for detecting Gravity-induced Loss of Consciousness (G-LOC) prognosis, pilots' interaction module, and pilots' context awareness platform. The algorithm for evaluating pilots' physiological stability uses psychomotor cognitive test (PCT) and heart rate variability (HRV) to measure pilots' mission performance before flight. The algorithms for detecting G-LOC prognosis utilizes electromyogram (EMG) to generate warning signal during flight. The pilots' interaction module was developed for pilots to operate the system efficiently under flight environment. The pilots' context awareness platform was designed for the system to process multiple sensor signals in real time. This wearable bio signal monitoring system is expected to enhance flight safety and mission performance of pilots.