The invention discloses an iterative demapping and decoding method and an iterative demapping and decoding system. The iterative demapping and decoding method comprises the following steps: step 1, a control unit and arithmetic units are initialized, wherein the arithmetic units comprise a demapper, a variable node decoder and a check node decoder; step 2, when the demapper reaches a starting condition, decoding procedures are started by the control unit; step 3, the decoding procedures are operated under the control of the control unit, at least part of the arithmetic units executes respective operation concurrently; and step 4, when a decoding stop condition is reached, the decoding procedures are stopped by the control unit, and code words of decoding results are output. The iterative demapping and decoding system comprises the control unit, a storer, the demapper, the variable node decoder and the check node decoder for achieving the method. The iterative demapping and decoding method and the iterative demapping and decoding system can solve the problems that operating efficiency is low, complexity is high, handling capacity is limited and the like in an actual system.