Provided is a method for finding a minimal signed digit with variable multi-bit coding. The method includes the steps of: scanning and grouping given multi-bit and checking the type of each group; deciding whether each group is to be performed by any one of a coding for positive number and a coding of negative number depending on the type of each group; converting the value of each group into a corresponding value of different number system and finding a signed digit based on the converted value; if the type of each group indicates the coding for negative number, performing bitwise inverting on the value of each group; and converting multi-bit subjected to the bitwise inverting into a corresponding value of different number system, and finding a signed digit based on the converted value.