Abstract: An irradiation facility with the type of sinkbox using cobalt target as its irradiation source and the requirement for the dose characteristics of 1E grade equipment irradiation test were introduced in this paper. The proper layout of reactor irradiated cobalt target was designed by the calculation program of dose rate distribution of radiation field, and the method of chemical dosimeter multi-point measurement was used to determine the dose rate distribution of the radiation field. The located place and irradiation dose rate of the irradiation sample were determined through the analysis of the spatial distribution of the irradiation field. Finally, the main factor and the assessment method of the total irradiation dose were provided. The results show that the performance of designed radiation field meets the requirement for the irradiation test within the full-size spacial scale, which is controlled within the range from 0.14 Gy/s to 0.42 Gy/s, and the maximum effective irradiation space is up to 1200 mm×1200 mm×1000 mm.