Abstract: The effects of the round edge beam hole on the frequency and wake field are studied using variational method, which allows for rounded iris disk hole without any approximation shape treatment. The frequencies and wakefields of accelerating mode and dipole mode are studied for different edge radius cases, including the flat edge shape that is often used to approximately represent the actual structure geometry. The edge hole shape has weak effect on the frequency, but strong effect on the wakefield. The study shows that the amounts of wakefields are not precise enough with the assumption of the flat beam hole instead of round edge. The shape assumption brings loss factor 15% err for the most dangerous EH16 mode.