Abstract: The hydrocarbon prospecting efforts in Alashan area should see from the angle of full-scale domain, on the basis of previous studies, by means of the data from geology, geophysics, drilling, etc., the basinal classification problem has to be dealt with first of all, i.e., properly proposing its structural units within the basin; secondly, providing its petroleum systems so that find out target zone in the whole systems including hydrocarbon generation, migration, accumulation, re-migration and re-accumulation. There exist two petroleum systems: Jurassic petroleum system in which oil reservoir with low productivity has been found, the key problem is to understand and determine the size of hydrocar-bon source area and hydrocarbon bearing abundance; Carboniferous petroleum system, the key problem is to understand and determine the conditions of cap rocks and the integrity of traps.

Key words: sedimentary basin, basic rock, aulacogen, source rock, oil and gas system