Abstract: Based on observed monthly surface air temperatures from the 73 stations in northeastern China from June to August during 1971-2011, the NCEP/NCAR reanalysis Ⅰ monthly height at 500 hPa and the NOAA extended reconstructed monthly Sea Surface Temperature (SST) V3b data during 1971-2012, and employing the statistical prediction idea of principal component regression (PCR), the paper constructed a seasonal forecast model of the modified PCR for classified summer temperatures in northeastern China using the atmospheric circulation and SST of January-May this year as predictors, which made a clear explanation on the early climatic causes of the Northeast summer temperature anomalies. Because of the qualities of smaller sampling errors, significant spatiality structure, but flexible time series of eigenvectors for the Rotated Empirical Orthogonal Function (REOF), the whole time-space series data of surface air temperature from 1971-2011 is analyzed by REOF for gaining full predictand information, the predictors are then diagnosed based on the relationships between REOF eigenvectors and preceding climatic conditions, and at finally the forecast model is built by the multiple stepwise regressions. The training period of the forecast model is the former 30 years of the time series, and the last 11 years in the time series are the period of the independenttest samples, in which the cross hindcast validation and independent test all showed skillful, especially effective for the classified temperature forecast.The preceding causes of summer temperature anomalies in northeastern China are able to be found by the processes of the built model, and the results show that the certain configured situation of AO/NAO, NPO, and subtropical zonal mode (SZ) of like-signed anomalous pressure in May is significantly responsible for the surface air temperature anomaly of southeastern Northeast in the following June; and the cooperation of AO/NAO, East Pacific Oscillation, and Eurasian pattern type 1 teleconnection wave in March is responsible for the following surface air temperature anomaly of northeastern Inner Magnolia and western Northeast in July; and subtropical zonal mode pattern associated with no apparent planetary wave trains in the mid-high latitudes in May is responsible for the surface air temperature anomaly in the portion of northeastern Inner Magnolia and the central and western part of Heilongjiang Province in coming August, with both of which located in northern Northeast; and, on the other hand, the causes of SST anomaly show that the anomalous SST distribution like El Niño (La Nia) pattern associated with the North Atlantic Tripole pattern in positive (negative) phase is significantly matched with atmospheric circulations leading to the lower (higher) summertime surface air tempertures in Northeast, and Indian Ocean Basin Mode(IOBM) in positive (negative) phase in late spring is related to the circulations leading to the higher (lower) surface air temperature in Northeast in August.