abnormal response phenomena in medium / longwave PC HgCdTe infra-red detector are discovered,which is entirely different from normal optical response law. In this paper, by numbers of experimental researches, existing conditions and characters of abnormal effects are confirmed. Finally, existing mechanisms of abnormal effects are discussed. This discovery has provided new clues and experimental sustainment for deep-seated cognition of physical structure, researches and app lications of new interactionalmechanism when materials are irradiated by laser.