Abstract: Fractu res of Chang 26 reservoir in Chuankou oil field are studied by use of the data of theoutcrop, cores, slices and the dip log. Main fractures, extending a long the direction of near EW, are small in size and poor-developed. Most fractures are closed underg round and will show the characteristics of open fractures by a rtificial excitation. So Chang-6¹. belongs to porosity reservoir . Chang-6¹ reservoir is 500～700m in depth. The minimum stress is vertical, and theoretically the hydraulic fracture should be horizontal. However, in fracture-developed areas, the hydraulic fractures may be vertical for the effect of natural fractures. Fractures have not shown the effect on the waterflooding by now.