1. A computer implemented data processing method applied in a data processing system for achieving iterative approximation of a target matrix, comprising: determining whether the target matrix corresponds to a low complexity condition by a determining unit of a data processing device; when the target matrix corresponds to the low complexity condition, driving an iteration unit with fixed-value parameters of the data processing device by the determining unit for obtaining a first updated target matrix according to a first variance and a first iteration parameter, wherein the first variance is relevant to a second iteration parameter, and the first and the second iteration parameters correspond to fixed values; and when the target matrix does not correspond to the low complexity condition, driving an iteration unit with unfixed-value parameters of the data processing device by the determining unit for obtaining a second updated target matrix according to a second variance and a third iteration parameter, wherein the second variance is relevant to a fourth iteration parameter, and the third and the fourth parameters are related to the target matrix.