A communication system and a codec method based on deep learning and known channel state information (CSI) are provided. The communication system includes: a first electronic apparatus including a known first link CSI and a CSI encoder having a deep learning function; and a second electronic apparatus including a known second link CSI and a CSI decoder having a deep learning function. The first and second link CSIs have a correlation or a similarity. The CSI encoder of the first electronic apparatus encodes or compresses the first link CSI into the first codeword, and feeds the first codeword back to the second electronic apparatus via a feedback link. The CSI decoder of the second electronic apparatus encodes or compresses the second link CSI into a second codeword, and decodes or restores the first link CSI of the first electronic apparatus based on the first codeword and the second codeword.