A data converting method and device therefor are disclosed by the invention, relating to data converting algorithm field, solving the problem of complicate data converting method in prior art. Steps of the invention are obtaining offset from the predetermined byte of the data string to be converted; obtaining the predetermined bits of data from the data string to be converted according to the offset; converting the obtained bits to decimal number; determining whether size of the decimal number is smaller than the first predetermined length, if so, keeping adding 0 to the upper digit of the decimal number till the first predetermined length is reached, and taking the data with added 0 as the converted data; otherwise keeping obtaining data from low bit of the decimal number, till the first predetermined length is reached, and taking the obtained data as the converted data. The method of the invention is mainly used for devices and methods requiring data converting, e.g. one time password generating method and device therefor.