Abstract: The correlation of datum cycle and reservoir quality of Middle Jurassic in Qiudong sub-sag of Taibei sag in Tuha basin is made. The analysis shows that the short-term elevation of Qiudong sub-sag is of distinct control on reservoir quality. With the datum rising, the reservoir quality becomes poor; contrariwise, it becomes good. Four types of the well log response models for the short-term datum cycle of Middle Jurassic are delineated such as retrogradation-retrogradation, retrogradation-progradation, progradationretrogradation and progradation-progradation ones. Also, with the mid-term datum rising, the braided river channel sand body is thickened, the sand grain size is getting coarser, with sand-shale ratio increasing. With the mid-term datum descending or cycling, the reservoir quality is getting poorer obviously. It is pointed out that the intervals with higher quality of reservoirs are corresponding to the reservoirs at the lower datum, so in Qiudong sub-sag, the Lower J2x4 and J2s2 could be favorable target zones vertically for lithologic oil-gas exploration; while two sides of its arc belt be advantageous zones laterally of developed lithologic oil-gas reservoirs.

Key words: Tuha basin, elevating, descending, sequence stratigraphy, reservoir space, datum