Through the analysis of a lightning protection scheme, the correct understanding of the nominal parameters such as discharge current and voltage protection level (〖WTBX〗U〖WTBZ〗p) in the lightning protection design scheme of the Surge Protective Device (SPD). Based on two types of products of SPDⅡlevel tests, comparing and analyzing the data in the test reports, it is found out that 〖WTBX〗U〖WTBZ〗p should be judged not only according to the marked value on the name plate of a SPD, but also determined by considering comprehensively the data in the test report of the SPD. So it is suggested that the manufacturers provide several 〖WTBX〗U〖WTBZ〗p values corresponding to the characteristic current values under the nominal discharge current values, according to the test reports, or provide a figure of the inrush current residual voltage curve in the product description to help users in understanding of the characteristics of SPD pressure limits.