Abstract: Observation data from 40 ground stations in China are used to evaluate the ground wind speed error of ERA5 and ERA5-Land reanalysis data with different resolutions. The results show that the mean bias errors (BEs) of the multiyear mean wind speed of ERA5 and ERA5-Land reanalysis data are 0.08 and −0.06 m s⁻¹, respectively; the maximum BEs are 0.46 and −0.19 m s⁻¹, respectively; the relative BEs (RBEs) are 4.4% and −2.0%, respectively; and the maximum RBEs are 33.0% and −10.1% respectively. Moreover, the slopes of the linear fitting equation of monthly mean wind speed are 0.93 and 0.97, respectively; the intercepts are 0.29 and 0.02 m s⁻¹, respectively; the correlation coefficients are 0.98 and 0.99, respectively; the mean root mean square errors (RMSEs) of the monthly mean wind speed are 0.17 and 0.14 m s⁻¹, respectively; the maximum RMSEs are 0.49 and 0.22 m s⁻¹, respectively; the relative RMSEs (RRMSEs) are 7.4% and 5.7%, respectively; and the maximum RRMSEs are 35.2% and 13.3%, respectively. The above errors in the high-resolution ground wind speed data of ERA5-Land is relatively low, which is conducive to improving the accuracy of wind energy resource assessment.