Abstract: The explorations and practices show that quantitative grain fluorescence technique (QFT) has unique advantages and characteristics in identifying the type of reservoir hydrocarbon inclusions and palaeo?fluid, detecting the migration pathways of oil and gas, and defining the oil?water contact. In this paper, the QFT is applied to the study of hydrocarbon accumulation and evolution in Mahe gasfield of Southern margin of Junggar basin, and good effects have been obtained. The research shows that there was mature crude oil filling in the early stage and a certain scale of paleo?oil pools had been formed in Mahe gasfield, and nowadays the condensate gas reservoir was formed by the fact that a great amount of high mature gas charging in late stage led to“Evaporating fractionation”of the original palaeo?oil pools. Meanwhile, the present gas?water contact was also shaped by late adjusting upward of paleo?oil?water contact on the basis of keeping the patterns of original paleo?oil pools