Abstract: To address voltage sag mitigation in "double-high" areas of new power systems, this paper takes Wuhan Optics Valley as the case. Based on measured data and electromagnetic transient simulation, the failure mechanism of grid-side centralized compensation devices under deep sags is revealed. Results show that under a 220 kV three-phase fault, user voltage drops by 85%–92%. The grid-forming SVG suffers virtual EMF collapse due to current limiter saturation, with voltage rise of only 0.4%, while the synchronous condenser equivalent overestimates by about six times. The Sag Mitigation Efficiency Index (SMEI) and a cooperative game allocation model are proposed. SMEI shows user-side DVR efficiency is nearly 10,000 times higher than SVG. The Shapley value gives an optimal cost-sharing ratio of 22% for the grid and 78% for users. The findings have been applied in Wuhan Optics Valley, providing decision-making tools for similar high-tech parks.