According to the causal analysis of building and internal system damage induced by lightning, in combination with the standard GB/T21714 Lightning Protection, it is found that that the damage probability (〖WTBX〗P〖WTBZ〗B and 〖WTBX〗P〖WTBZ〗SPDof GB/T21714.2) is related to the probability distribution of lightning current and the extreme value of lightning current, which corresponds to Lightning Protection Level (LPL). The value of 〖WTBX〗P〖WTBZ〗Bequals to the sum of the probability of the lightning current greater than the maximal lightning current and the probability of the lightning current less than minimum corresponding to LPL; the value of 〖WTBX〗P〖WTBZ〗SPD  equals to the probability of lightning current greater than maximal lightning current corresponding to LPL. It is pointed out that for the damage probability (〖WTBX〗P〖WTBZ〗B and 〖WTBX〗P〖WTBZ〗SPD in GB500572010) at various lightning protection levels, the values stipulated in GB/T21714.2 should not adopted directly, rather computing according to the lightning current parameters given in GB50057, or using the information sources on the lightning detection network to obtain the data of cloudtoground lightning within a certain scope nearby the building, so to calculate the probability distribution function of lightning current and further the value of 〖WTBX〗P〖WTBZ〗B and 〖WTBX〗P〖WTBZ〗SPD by the abovementioned probability distribution function of lightning current.