Abstract: A multi-granularity parallel FFT computation device including three memories, a butterfly computation device, a state control unit, a data reversing network and a first selector. The three memories are each a multi-granularity parallel memory, and store butterfly group data and twiddle factors corresponding to the butterfly group data. The butterfly computation device perform computations of a butterfly group based on the butterfly group data outputted from the first selector and the corresponding twiddle factors outputted from one of the memories, and write a computation result back to the other two memories. The device can read butterfly group data and corresponding twiddle factors in parallel from the multi-granularity parallel memories with a specific R/W granularity. No memory conflict will occur in the read operation, and no additional process is required for sorting the read/written data.