Reasonable design of the cavity shape of the damping hole effectively reduces the leakage rate of the hole-pattern damping seal (HPDS). A novel HPDS with dovetail-like diversion grooves was proposed, and the geometry outline of the dovetail-like diversion groove was described by using the hyperelliptic curve. Computational fluid dynamics commercial software was used to simulate the three-dimensional flow field of the dovetail-like hole-pattern damping seal (D-HPDS). The leakage characteristics of the damping seals with a typical circular hole, leaf-like hole, and dovetail-like hole were compared numerically and experimentally. The three-velocity zone model of HPDS was proposed to reveal the mechanism of leakage reduction effect of the D-HPDS compared with typical circular hole-pattern damping seal (C-HPDS). The influence of operating parameters and key geometric parameters on leakage characteristics of the D-HPDS was studied. The results show that the leakage rate of the D-HPDS can be reduced significantly in a wide range of operating conditions and seal clearance compared with the typical C-HPDS, and the maximum reduction amplitude of leakage rate reaches up to 25% at a relatively small pressure ratio. The main reasons for the leakage reduction of the D-HPDS can be explained by the fact that the change of outflow direction from the cavity induced by the interaction effect of adjacent cavities, further resulting in the formation of turbulent vortex in the cavity and the low-speed flow zone in the sealing gap. For the design goal of low leakage rate, the inclined angle of the dovetail-like diversion groove is appropriate between 45 deg and 55 deg, the tip extension ratio is appropriate between 0.8 and 0.95.