A method for arranging memories of a low-complexity low-density parity-check (LDPC) decoder and a low-complexity LDPC decoder using the same method are provided. The main idea of the method for arranging memories of a low-complexity LDPC decoder is to merge at least one or two small-capacity memory blocks into one memory group, so that the memory area can be reduced and the power consumption in reading or writing data is lowered. Besides, as the merged memory group shares the same address line in reading or writing data, at least one delay unit is used to adjust the reading or writing order and thereby ensure data validity. A low-complexity LDPC decoder using the disclosed method can meet the demands of high processing rate and low power consumption.