Abstract: The Cambro-Ordovician is very thick and widely distributed in Tarim basin. The well developed palaeokarst feature in it is due to multistage tectonic movement and its intrinsic sedimentary characteristics. It is the palaeokarst distributed vertically and laterally that controls the hydrocarbon distribution. More than ten large-and middle-scale such oil-gas fields have already been found up to now. This paper highlights the stage of palaeokarst development, the distribution, type and origin of palaeokarst and the characteristic and the oil-controlling effect of such a reservoir. It is concluded that the Cambro-0rdovician system(@) in Tarim basin is significant horizon(s) or zone (a) for finding out giant oil-gas field in future.

Key words: Tarim basin, Cambrian, Ordovician, carbonate rock, palacokarst, reservoir, oil-gas field