The invention relates to an iterative timing synchronized method and a device based on soft decision information (SDM) of low-density parity-check coding (LDPC) and belongs to the technical field of digital communication. The invention is characterized by making use of the soft decision information in the low-density parity-check coding to realize timing synchronization. The content of the invention is as following: firstly, after signals received from the system are processed with high power sampling, interpolation and matching with wave filtering by a data receiving and processing module 1, the low-density parity-check code frame originating serial number is obtained from a low-density parity-check code frame synchronous detection module and synchronous processing is triggered; secondly, the invention uses an iterative timing capturing module 2 to realize iterative timing capture, and then the invention uses an iterative timing tracking module 3 to realize iterative timing tracking; finally, the invention uses an iterative timing control module 4 to judge and switch timing capturing and tracking, and controls the final coding data of a low-density parity-check coding module outputting system . The invention can be applied to the timing synchronization with low signal-to-noise ratio and high-speed digital communication and in particular to be suitable for occasions with low signal-to-noise and the occasion of deep space communication and high-speed magnetic recording system, etc.