Abstract: Reservoir stress is caused by both gravity and tectonic movements The well pattern for oil-and-gas development is considerably constrained by distribution of reservoir stress，particularly in the reservoirs with low permeability. In this paper，we wil1 prensent the results of an investigation on the distribution pa tern of modern reservoirs stress of the Toutai Oilfield based upon in situ measurements，core observations，laboratory work and numerical simulation The maximum principal stress(artificial fracture)in the horizontal plan of the Toutai Oilfield is directed N100°～ 120°E with a mean of Nll0°E，and the natural fracture between NO°～ 50°E. The southern part of the oilfield has smaller reservoir stresses in three directions than the northern part. The direction of structural faults is almost parallel to that of natural fractures. Therefore，a reasonable wel1 pattern cutting the water flood wel1 pattern should be designed to be 300m ×300m and at 45° to artificial and natural fractures. Waterflood pressure should be smaller than the minimum principal stress，and the technique of unstable intermittent waterflooding should be adopted.