Abstract: Most of the surface contamination detection equipments use a phoswich detector composed of ZnS(Ag) and plastic scintillators to simultaneously measure α/β rays, and the discrimination method of α/β rays is critical in this process. The traditional discrimination methods are pulse amplitude discrimination and pulse width discrimination, and the parameter setting of the analog components has a great impact on the stability of the discrimination. In this paper, a digital pulse processor is used to screen α/β rays. A current restorer, a doublechannel box filter and a ratio calculator inside the FPGA were constructed to calculate the ratio output peaks of the doublechannel box filter. The α/β rays are Gaussian in different intervals in the ratio statistical graph, thus the α/β rays can be discriminated. The results show that this discrimination method can discriminate α/β rays in real time, with the quality factor of 3.52 and crosstalk ratio of less than 0.5%. The detection efficiency for α and β rays is respectively no less than 57.7% and 37%.