A slope area is one of the important structural units in a rift-subsidence and sag basin. According to the fault property and depositional thickness, a slope is divided into two kinds: complex slope and simple slope. The western slope of the northern Songliao Basin is a simple slope that is characteristic of few faults and low dip. Through an analysis on the condition of migration and accumulation, we think that a simple slope has its special character. This special character is reflected in three aspects: the first is that crude oil in a simple slope is not original, and mainly come from near sag, oil and gas migrate laterally in the narrow path through sands in the main passage, and oil and gas distribute linearly. The second is that big structural traps are not many in a simple slope and mainly microstructures develop. Traps in a simple slope mainly contain Stratum traps and lithologic traps, and their distribution is controlled by structural belts. Traps in a overlap area are lithologic pinchout traps, and traps in a nose structure that is controlled by big faults mainly developed barrier faults traps and structural-lithologic traps. Traps in a nose structure that is not controlled by big faults mainly developed structural-lithologic traps. The third is that a simple slope is universally suffered by leaching of atmospheric rainfall. Because free oxygen with atmospheric rainfall percolates into reservoir, crude oil is transformed into heavy oil by oxidative degradation, and heavy oil is distributed universally. The special condition of migration and accumulation decide the accumulation of oil and gas. Oil and gas were accumulated in the traps in the migration pathway and in sandstone lens in the non-main passage by small faults. In a simple slope the exploration targets are the structural-lithologic reservoir(small scale) in the microstructures and fault reservoir(Middle scale)surrounding a large fault and lithologic pinchout oil reservoir in a stratigraphic overlap zone in the migration pathways on the basis of research on the stratigraphic sequence.