Climate extremes are intensifying under global warming, posing unprecedented challenges to ecosystems, water resources, and human societies. However, high-resolution, basin-specific extreme climate datasets remain scarce, particularly in climatically diverse regions like China. Here, we present ECHIDNA (Extreme Climate Historical and Future Indices Data under Numerous Approaches), a comprehensive database of 33 ETCCDI indices derived from an ensemble of eight CMIP6 Global Climate Models (GCMs), statistically downscaled using seven methods including CDFt, ECDFM, ISIMIP, LS, QDM, QM, and SDM. Covering 1979–2100 under three SSP scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5), the dataset focuses on four major river basin regions: the Yangtze River Basin, Yellow River Basin, Hai River Basin, and Southwest River Basins. Evaluation using PCC, NSE, KGE, and RMSE demonstrates significant improvements in capturing temporal variability and extreme event intensity compared to raw model outputs. By incorporating multi-model projections, ECHIDNA enables robust assessments of uncertainty in future climate risks and supports hydrological, agricultural, and infrastructure resilience planning. It is openly available to facilitate climate impact studies, adaptation strategies, and international research collaboration.