Abstract: This paper is based on the macrofossil plants of Larix gmelini Rupr.and L.olgensis Henry and abundant pollen,spores,and green algae of 2 peat samples obtained from digging a irrigating canal at Chuangye farm(6.5m and 3.5m deep below the surface)in Sanjiang plain.About 36000 years ago Sanjiang plain was covered by cold-temperature needleleaf deciduous forest,prodominant of Larix spp,, Betula,herb and green algae.The climate of Sanjiang plain was rather humid and cold,with an annual mean precipitation higher than that of the present. The lakes and marshes were developed.According to the information of macrofossil and palynoflora,we hold that in the last-glacial,Larix,Abies,Picea,Betula forests became predominant in the Sanjiang plain.Therefore,the development of marshes in Sanjiang plain has been rapid since late Pleistocene.