The scientific application of psychological testing technology has an irreplaceable role to play in the investigation and adjudication of difficult cases. In order to ensure that this technique plays a role in the investigation and trial of difficult cases, it is necessary to adhere to a scientific attitude, to be guided by the theory of psychological science, to follow the laws of psychological activity, and to fully recognize the complexity and diversity of the factors affecting the test, so that the technique of psychological testing can be correctly used. The cognitive comprehensive test verifies and screens the relationship between the suspect and the case and the cognitive case by detecting the presence or absence of the corresponding cognition, and is therefore a more scientific, objective and reliable test method at home and abroad, which is also the reason why it has played a significant role in the detection of all kinds of difficult cases and backlog homicide cases. In this paper, through the cognitive comprehensive test in the backlog homicide cases investigation, the scientific application of psychological testing technology to talk about some views.