A series of reliability design work is carried out for a scintillation detector which can detect pulsed neutrons in complex environment. In the design, the inherent reliability of the detector is improved by means of redundant backup of test channels and anti-vibration design. The mission reliability objectives of each component of the detector are defined by means of reliability modeling and index assignment. Through FMECA analysis method, the failure modes and their effects of each component of the detector are studied, and the important component of reliability is determined. The reliability of the detector is further improved by using environmental stress screening test and reliability enhancement test. It is proved that the mission reliability of the pulsed neutron detector with the above reliability design assurance technology is not less than 0.999.