A method for controlling a peak current is provided. The method first uses a plurality of registers to encode a plurality of states of a circuit and generates an original state code. Then, the original state code is re-encoded to reduce the difference between the sum of charging current of the charged registers and the sum of discharging current of the discharged registers while the registers are switched among the charging/discharging states. Finally, a standard technology library is read and logic circuit synthesis is performed for the re-encoded state codes.