Abstract: Based on the adjoint transport technology, the ex-core detector response function under the full power operation of one third-generation reactor is calculated by using the two-dimension SN code. Calculation results are compared with the original data, and the radial weighting factors would not exceed 3%, and the axial weighting factors would not exceed 1%.The result of this calculation proves that the calculation model and method is correct. The technology has been validated in the Ling’ao Phase II Nuclear Power Plant. Compared to the numerical result of the radial weighting factors via SN forward Transport Method, it shows that the calculation results difference of the two methods would not exceed 5%. It proves that the result for the two methods is identical and the computational efficiency of the Adjoint Transport Method is more efficient.