Abstract: The life of Mimjiang Test Reactor (MJTR) detectors and its control system will be shortened due to the nearby strong neutron and γ irradiation in the core. With the enlarging of the diameter of the irradiation channel in the reactor, the changing of the center location of the channel and the increasing of the volume of irradiation sample, the disturbance to the neutron signal received by the detectors will be increased, which is harmful to the safe operation of the reactor. Thus the layout of MJTR detectors is improved. This paper introduces the measures, design principle and methods and result for the improvement of the layout of the detectors. Debugging results indicate that the layout of the detector channels and function assignment in the improved design are reasonable, and can meet the design requirements.