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Experimental results show that a significant fraction of current will be carried by the ablated plasmas and the current flow through the precursor column strongly depends on the inter-wire gap1. It has been found that the ablation rate of wire core is axially non-uniform. When gaps appear in the wire cores, the plasmas prefilled inside the arrays begins to implode. The ablation dynamics determine the initial distribution of mass and current density of implosion so it plays an important role in the eventual x-ray production of the pinch. The basic processes of wire-array ablation on 20MA Z machine are similar to that on the low current facilities such as MAGPIE2 and COBRA3. The dynamics of ablated plasma of cylindrical wire-array Z-pinches are studied numerically in (r, θ) geometry by using 2D MHD simulation model, in which mass injection boundary conditions are presented. The 2D spatio-temporal distribution of plasma parameters and magnetic field are obtained. The ablated-plasma dynamics contain several processes: drifting toward the axis, arriving at the axis and forming the precursor plasma column, contraction and expansion of the precursor column, which is fundamentally reasonable. The relationship among the ablation velocity, the ratio of ablated plasmas to the total wire-array mass and the initial array load parameters is analyzed, and the results is in reasonable agreement with the experiments on the MAGPIE facility. Furthermore, the results of 2D MHD simulation of precursor current and mass ablation rate in wire array Z-pinches on the Qiang Guang-I facility4 are presented. The effects of the initial interwire separation on the structure of magnetic field are investigated and the results can make valuable suggestions to design wire array Z-pinch loads.