A Plenty of aerial vehicles would make plunging oscillation motions, which fly with moving wings or encounter gusts at low Reynolds number conditions. The flow field around the vehicles and the force coefficients dramatically vary with the unsteady motion parameters (mean angle of attack, reduced frequency and amplitude). The paper investigates the effects of such parameters on the aerodynamic characteristics of a plunging NACA0012 airfoil. The Computational Fluid Dynamics (CFD) solver based on the Finite Volume Method (FVM) is applied, the governing equations of which are the unsteady, incompressible two-dimensional Navier-Stokes(N-S) equations. The airfoil performs sinusoidal plunging motions at the Reynolds number 2.53 × 105. A detailed analysis of the instantaneous and mean force coefficients versus the angle of attack and time during plunging oscillations are presented. The analysis shows that these parameters change the instantaneous force coefficients quantitatively and qualitatively. With the increase of kH, the maximum efficient angle of attack reaches 55o and the lift coefficient achieve 6.0, although it exceeds the deep dynamic stall angle of attack seriously. It is also observed that the strength, interaction, and convection of the vortex surrounding the airfoil are significantly affected by the variations of these parameters.