Abstract: The design principle of tissue equivalent ionization chamber based on the theory of recombination was described, and the area neutron and gamma dose equivalent instrument was designed. This detection system can indirectly acquire the information of the ambient dose equivalen, the absorbed dose and the quality factor of the mixed radiation field using only one probe. Moreover, the detection system was tested by the accelerator and the standard radiation field. The results indicate that the system has good energy response and sensitivity to the neutron and gamma radiation, especially to the high energy gamma radiation and the neutrons with energy ranging from thermal to dozens of MeV. The uncertainty can be controlled within ±50%, while the dose rate of the radiation is above dozens of μSv/h, so this detection system can serve as the necessary measurement instruments and monitoring technology for the places having the mixed radiation field of neutron and gamma ray.