Abstract: Ex-core detector response function represents the contribution to the detector tally from each reactor core assembly, reflects the relationship between reactor core power distribution and detector tally. In this paper, the adjoint transport calculation by three-dimensional discrete coordinate method (SN) program TORT was researched, and a post-process code to achieve the conversion between three-dimensional adjoint flux and PWR fuel assembly response functions was developed; Based on the CAP1400 reactor model, its ex-core detector response functions were analyzed, and the results match well with the TORT forward calculation results. Through the research of this paper, three-dimensional distribution calculation of PWR plant ex-core detector response functions was achieved.