Abstract: In this paper, the criterion of establishment and withdrawal of East Asian summer monsoon in Northeast China is suggested by using NCEP/NCAR reanalysis daily date and daily precipitation from 80 observation stations of Northeast China for the past 20 years. When the pentad-averaged contours of θse 336 K and 4 m/s south wind at 850 hPa along 122.5 °E time-latitude cross section are across 40 °N together, the pentad is defined as the established time of East Asian summer monsoon in Northeast China. The total pentads of persistency and accumulation are effective days. Apentad is defined as the withdraw of East Asian summer monsoon from Northeast China when the pent adaveraged θse 336 K contours withdraw to the south of 40°N. If the pentad-averaged contours of θse 336 K and 4 m/s south wind are not across 40°N at the same time, it is defined that this is an un-est ablishment year of East Asian summer monsoon in Northeast China. The time table of establishment,persistency, accumulation and withdraw of East Asian summer monsoon in Northeast China in 1980~2000 is given. We find that the established time is the 41th pentad (5th pentad in July), accumulated effective time is 3.6 pentads (about 18 days), and withdraw time is the 45t h pentad (3rd in A ugust). The precipitation increases (decreases) clearly around the establishment (withdrawal) time of East Asian summer monsoons in Northeast China as the change of water vapour convergence. The strong summer monsoons defined in this paper, such as 1981, 1988, 1990, and 1994, are basically accordance with others defined. The streamline and heating fields in the years of East Asian summer monsoon's establishment and un-establishment in Northeast China are analysed, and the difference is significant. In the establishment year, the Northwest Pacific High is westw ard and northward (about 7 longitude and latitude) and no blocking high in East Asia mid-high latitude. It is opposite in the un-establishment year. In 1994, a strong summer monsoon year, the positive anomaly heating center at 200 hPa is tow ards tropical South India Ocean, West Pacific warm poolis a relative cool area, and the anomaly divergent wind Vx gradient is strong along the East China coast. But in 1980, an un-establishment summer monsoon year, the thermal difference between sea and land in North Hemisphere is relative weak, and more un-clearer in low tropopause.