Abstract: In order to further understand the past temperature variation over Common Era in the Northern Hemisphere(NH), we reconstructed the NH annual temperature variability over Common Era using the optimal information extraction(OIE)method, based on 16 tree-ring chronologies longer than 2000 years.The proxy dataset is composed of 15 tree-ring width chronologies and one tree-ring density chronology covering a large area extending across the Northern America, Europe, and Asia. All chronologies are strongly correlated with the multi-proxy reconstructed annual NH temperature anomalies over the past millennium at the 95% confidence level. The OIE method utilized the ensemble LOCal regression method to improve the ability to retain the low frequency signal, and used the correlation coefficient between the calibrated sequence and the local climate factor in the proxy record location to measure regional differences response to the climate signal. This method belongs to the Composite-plus-scale method classification.The results show that there are one extreme low temperature event and four extreme high temperature events, 50 low temperature events and 53 high temperature events, two cold periods and three warm periods over the past 2000 years. Among them, 8 low temperature events occurred in the first cold period(ca.500~550A.D.), one extreme low temperature event and 38 low temperature events appeared during the Little Ice Age(1450~1850A.D.). In addition, there are 17 high temperature events in the Medieval Warm Period(900~1250A.D.). Before 1000A.D., there is a warm period in ca.400~500A.D., during which existed one extreme high temperature event and 11 high temperature events. The third warm period is the 20th century, during which extreme low temperature and low temperature events did not appear but there have been two extreme high temperature events and 21 high temperature events. This implies that the extreme low and low temperature events over a hemispheric scale could not likely appear under further global warming scenario.Based on the attribution analysis of the reconstructed temperature variability, the forcings, including the Atlantic Multi-decadal Oscillation(AMO), solar activity and volcanic activity all could have affected the NH annual temperature anomalies variability over the past 2000 years. The AMO explains more than 36% NH temperature variability over multi-decadal time scale indicating that the AMO is the main driving factor of the NH annual temperature variations over the past 2000 years. Note that the tree-ring chronologies used in this reconstruction and in AMO index reconstruction may derive from the same positions. This similarity would cause the uncertainty in the influence of AMO on the NH temperature. This needs to be verified using the new AMO index based on the other type proxy records, e.g. coral record. Solar activity could have weak impact on the NH temperature variability on a centurial time scale. Compared with 34 stronger global volcanic events, the NH temperature obviously drops in the first year after the eruption. This cooling effect completely disappeared in the fourth year. This implies that the impact of the volcanic activity on NH temperature decrease is transient and takes effect only on the inter-annual time scale, which is consistent with other results.