Integration of climate proxies and development of hemisphere-scale temperature reconstructions of the past millennium has been the focus of global change research.It not only helps to place contemporary climate variability in a long-term perspective,but also to improve our understanding of the spatial and temporal patterns of long-term climate variability and relevant forcing mechanisms of long-term and recent climate changes.Large-scale millennial length regional and Northern Hemisphere climate reconstructions have made considerable progress over the past 20 years,especially in recent years.This is mainly represented by the gradual development of new datasets,the improvement of reconstruction methods,scientific knowledge of spatio-temporal characteristics and its driving mechanism of climate variability on various timescales from annual to millennial,and the diagnosis of historical status of climate warming in the last decades.The scientific basis of knowledge of ongoing warming mechanism and future climate projections of the 21st century are forming.We summarized the achievements of last millennium and Common Era climate reconstructions with respect to methodologies for last millennium climate reconstructions,research history and present scientific knowledge of climate variability at decadal to centennial timescales,and suggested future research directions.