An implement method of a FFT processor comprises the following steps. First, a 21 point FFT processor, which has an output and an input receiving a 2n+1 point data, is provided. A 2n-point FFT processor having an input and an output is provided. Sequentially, a multiplexer, which has a first input coupled to the output of the 21 point FFT processor, a second input receiving a 2n point data and an output coupled to the input of the 2n point FFT processor, is provided. When an input data is a 2n point data, the second input of multiplexer is coupled to the output thereof, and when an input data is a 2n+1 point data, the first input of multiplexer is coupled to the output thereof.