A method for calculating a number of proof-of-work to measure how much work has been done in one block mining, includes the following steps: using a low hash, wherein the low hash value corresponding to a low nonce is not greater than a predetermined target value; using a high hash, wherein the high hash value corresponding to a high nonce is higher than the same target value; and calculating the number of proof-of-work according to the low hash value and the high hash value. The low hash value is the lowest hash value in one block mining. The high hash value is the highest hash value in the same block mining.