Abstract: The fractured-vuggy petroleum reservoir is the dominant Ordovician reservoir in Block 4 of Tahe Oilfield. The fracture is the major petroleum migaration system and accumulating space. Through an observation on the core and thin section of more than 20 wells, combined with image logging and other analysis and test data, this paper studied some characteristic parameters of reservoir fracture, such as dip angle trend, length, and backfilling feature. On this basis, the formation of fracture is divide into four periods. The approach of core and outcroup comparison is adopted to study the effect of fracure features to karst and the effect of fracture to reservoir properties.