Abstract:The concentration of greenhouse gases continued to increase in 2017, and the global mean temperature was 1.1℃ above the pre-industrial levels, making the year 2017 become the second warmest year on record and the warmest year not influenced by El Nino event. The cryosphere continued its contraction. The maximum sea-ice extent of Arctic sea in winter broke the lowest record while the sea-ice extent of Antarctic was near the record low level throughout the year. Global sea surface temperatures were significantly above the 1981-2010 average, and the global mean sea level kept rising steadily. The ocean heat content reached new record highs due to the intensified impact of ocean acidification. Many significant weather and climate events occurred in 2017, including a very active North Atlantic hurricane season, major monsoon floods in the Indian subcontinent, severe droughts in East Africa as well as some torrential rains, heat waves, cold waves and severe convective weather at regional or local scale worldwide. Econo-mic losses from the weather and climate related disasters set a new record in 2017. This paper summarizes the major events and its impact in 2017, and analyzes the formation causes of typical events including the exceptionally destructive hurricanes that occurred in rapid succession in the North Atlantic and the significant summer heat waves in the United States. Analysis of atmospheric circulation and external forcing shows that the positive SST anomalies of Caribbean and western tropical Atlantic enhanced the convective activity and decreased the vertical shear of wind speed, providing favorable background conditions for the development of hurricanes. In addition, the stage weakening of North American subtropical high caused four destructive hurricanes to make landfall successively in southern United States and the Caribbean region. In early July, the North American subtropical high that was influenced by the eastward extension and enhancement of subtropical westerly jet and the maintaining of Northeast Pacific cut-off low continued controlling the southwestern United States. This was the major reason for the summer heat wave on the west coast of the United States.