A decoding method, a memory storage device and a memory control circuit unit are provided, the decoding method includes: reading a plurality of memory cells according to hard decision voltage to obtain hard bit; performing a parity check procedure for the hard bit to obtain a plurality of syndromes; determining whether the hard bit has error according to the syndromes; if the hard bit has the error, updating the hard bit according to channel information of the hard bit and syndrome weight information corresponding to the hard bit.