The invention discloses a decoding method for a blocky check code with low density and a multi-mode reconfigurable decoder, and particularly relates to a decoding design based on the blocky check array of a unit cycle permutation array; the decoding method adopts partly collateral minimum and bias iterative compensation algorithm, and is characterized by low complexity and fast iterative convergence; the decoder has flexible configuration and high availability of resources, and the decoder is characterized in that: firstly, the decoder can support the blocky check array decoding with different code lengths under various code rates; secondly, the decoder can select and configure different messages to update concurrent factors according to the decoding delay and the throughput requirements; thirdly, node messages are stored in a distribution type, the write / read access control is easy, and the node messages are stored in a compression type, thereby effectively improving the utilitization of the stored resources; lastly, the iterative update adopts multi-level production line structure, thus fully improving the data throughput of the decoder. The method and the device of the invention have the advantages of stable performance, flexible configuration and good expansibility, etc.