Abstract: In response to the growing terrorist activities, a security check instrument for explosives detection based on associated particles technique (APT)/neutron time of flight(TOF) has been developed. This paper describes the instruments working principle and the development of his process. The instrument can be remotely controlled from any PC-compatible computer. Inside is an APT neutron generator with a 33 matrix of semiconductor detectors of associated alpha-particles, the shielding protection system of neutron and gamma-ray, support platform, arrayed NaI(Tl)-based detectors of gamma-rays, fully-digital data acquisition electronics, data analysis and decision-making software, and transmission device. The common explosives and chemical warfare agents were detected by security check instrument. Results show that the instrument can meet the needs of practical application. The instrument is mainly used to detect explosives in luggage at check routeway, and it can also be trained to detect other hazardous materials, such as chemical/toxic/drug materials, if their chemical composition is in any way different from that of the surrounding materials.