The invention provides a block balancing method for an orthogonal frequency division multiplexing (OFDM) system on the condition of a fast time variant channel. The method comprises the following: at a sending terminal, a bit signal subjected to cyclic redundancy codification is subjected to channel codification, interlacement, symbol map, serial / parallel conversion and IFFT conversion to be converted to a time domain signal; the time domain signal which is subjected to serial / parallel conversion and is inserted with a cyclic prefix is sent to a radio channel; at a receiving terminal, the signal is received by a traditional first-order frequency domain equalizer, and the signal guess value is checked after the signal is subject to serial / parallel conversion, demap, deinterlacement and signal path decoding; if the check is correct, the signal is outputted; if the check is not correct, the block balancing process is performed, during which, firstly, a time domain OFDM sending signal is restructured; secondly, the received time domain OFDM symbol is divided into a plurality of equilong signal receiving subblocks, the loop restructuring and the interference removing processes are performed by a time domain OFDM restructured signal; and finally, each subblock is subjected to frequency domain balance, the balanced guess values of sub blocks are merged to obtain the block balance output serving as the input of the serial / parallel conversion.