On the opening delay of a discharge reed valve for compressors caused by the oil film in the clearance between the reed and the valve seat, effects of design conditions on the opening delay are analyzed through the experiment and the numerical simulation. Investigated are three kinds of conditions, the time rate of the bore pressure (compression speed), the oil viscosity, and the thickness of the reed. The experiment shows that the over-compression by the delay increases with increasing each of three condition values. The simulation reproduces qualitatively the effect of the bore pressure rate on the delay. The smaller bore pressure rate makes, under a certain bore pressure, the larger film thickness or the larger cavitation bubble diameter that results in the oil film rupture and the valve opening under the smaller bore pressure. The simulation also reproduces qualitatively the effect of the reed thickness. The larger reed thickness with the larger bending rigidity leads to the smaller reed deformation, the smaller oil film thickness, and the longer delay. On the oil film viscosity, the simulation fails in reproducing the change in the delay. The fail is due to the change in the oil film thickness of the simulation being smaller than that of the experiment. The experiment and simulation results indicate that, on all three conditions, the change in the increase of the oil film thickness leads to the change in the valve opening time and thereby the over-compression.