Aiming at the deficiency of reliability design for traditional airborne fire-detecting system, the optimization design is carried out in this paper from four aspects: fire-detecting system architecture, fire detection circuit, data security strategy and built-in self-detection. An improved fire-detecting system architecture is proposed, which effectively reduces the transmission links of fire information and significantly improves the reliability of fire detection and fire alarm tasks. The full bridge conditioning mode is adopted to realize the detection of the full resistance range of the fire sensor, which increases the pollution detection capability of the fire sensor, and a high-reliability BIT detection circuit is designed to realize the online fault diagnosis of the system in the whole working cycle. At the same time, the security data strategy is designed for the information transmission process, which can effectively improve the confidence and reduce the false alarm rate. Both theoretical analysis and test results verify that the reliability of alarm task and the reduction of false alarm rate of the optimized fire-detecting system have been significantly optimized and improved. Furthermore the scheme can improve the accuracy and reliability of the fire-detecting system and enhance the safety of the aircraft.