A transceiver used for an orthogonal frequency-division multiplexing (OFDM) system is provided, including: a signal processing device for receiving an OFDM symbol and processing the OFDM symbol to generate a processing signal according to the OFDM symbol, wherein the OFDM symbol having pilots which have been hierarchically modulated; a pilot signal analysis device for collecting the processing pilots of the processing signal and demodulating the processing pilots to generate a plurality of levels where one of the plurality of levels comprises a plurality of refinement bits; a degree difference analysis module for generating a plurality of degree differences according to the refinement bits and detecting channel classification according to the degree differences to transmit a channel classification signal; and a channel detection module for generating and transmitting a best modulation indication signal to another transceiver to adjust modulation scheme according to the channel classification signal.