MOV is the core component of the SPD. According to the regulations of IEC 61643, the discharge current capacity of MOV is an important indicator of SPD’s antithundering capability. Usually, the maximum discharge current of MOV is considered as its discharge current capacity. But this does not mean that the maximum discharge current of MOV represents the discharge current capacity of MOV. In order to further and accurately analyze SPD’s antithundering capability, it is necessary for researchers to upgrade the measurement of the discharge current capacity of MOV. By studying the attributes of discharge current capacity and introducing the implication of AS Resources, the differences between the maximum discharge current and the discharge current capacity are distinguished. The discharge current capacity of MOV can be better measured by using AS Resource theory. The optimized method can evaluate SPD antithundering capability more accurately.