The invention provides an S box evolution generator which comprises a random source, more than two different conversion parts, a cryptology index computing and judging part, a threshold judger and a buffer. The evolution generation process comprises the steps of: initializing stored contents in the buffer into unit replacement; generating random numbers by the random source, sending the stored contents in the buffer into one of conversion parts according to the values of the random numbers; sending a conversion result into the buffer after one of the conversion parts is converted, simultaneously sending into the cryptology index computing and judging part for computing a cryptology index and judging whether the index of the conversion result is qualified or not; if so, clearing the conversion times, outputting the conversion result to be used as an S box generated by the evolution; if not, adding 1 into the conversion times; and then in the threshold judger, comparing the conversion times and the preset threshold, if the conversion times are small than the threshold, returning to continue the evolution until the conversion times reach the threshold and resetting the contents of the buffer into the unit replacement.