Abstract: Previous studies indicate that surface wind speed (SWS) over China is declining continuously during past decades under global warming, and this has significant impact on wind energy resources. Based on a series of researches, spatial and temporal characteristics of SWS and its main causes are discussed. Overall, the SWS over China significantly weakens during the past fifty years. The average decreasing rate is 0.1-0.22 m·s^-1 per 10 years, but there are obvious differences in season, region and wind speed. The largest decreasing rate occurs in spring and winter while the smallest occurs in summer. Wind speed of north and east coast areas dropped more sharply than southwest. Furthermore, top percentiles of wind speed dropped more sharply than the bottom percentiles. The change of large-scale pressure gradient force (PGF) is a direct cause of the decrease of SWS, and climate warming exacerbates the weakening of PGF. This is mainly due to increases of surface temperature in the middle and high latitudes of Eurasia continent, which is more significant than that in low latitudes and the western Pacific. In particular, the weakening Siberian high (SH) caused by warming reduces the PGF between land and the adjacent ocean, which is the main factor leading to the weakening of the East Asian winter monsoon (EAWM). For the deficit of East Asian summer monsoon (EASM), phase transition of the Pacific decadal oscillation (PDO) and the Atlantic multi-decadal oscillation (AMO) from cold/warm to the opposite is the main cause, and surface cooling of East China Plain caused by the aerosol radiation effect may also play an important role. Besides, some researches indicate that aerosols can reduce the EAWM through thermodynamic process. Thus, the variability of East Asia Monsoon is the result of synergistic effects of climate factors at different spatial and time scales. Controlled experiments show that the SWS of China will decline more sharply as the greenhouse gases (GHG) emission increases. The weakened SWS influences wind energy development significantly, low speed wind technology boomed, and more wind farms will be developed in low latitudes as regions with abundance wind resources in North China experienced severe SWS deficit. To assess risks precisely, confidence probability of long-term electricity production should be considered during the decision making process of the investment of wind farms.