The dynamics of ablated plasma of wire-array Z-pinches are studied numerically in (r, θ) geometry by using 2D MHD simulation model, in which plausible mass injection boundary conditions are incorporated, and 2D spatio-temporal distribution of plasma parameters and magnetic field are obtained. The ablated-plasma dynamics involves 4 stages: drifting towards the axis, arriving at the axis and forming the precursor column, contraction and expansion of the precursor column, which is essentially reasonable. The relationships between the ablation velocity, the ratio of ablated plasmas to the total wire-array mass and the initial array load parameters are analyzed, and the results are in reasonablly good agreement with the experiment. The effects of the initial inter-wire separation on the structure of magnetic field are investigated and the results can give valuable suggestions to designing the wire array Z-pinch loads.