To study the diagenetic regularity and influencing factors as well as control action of diagenesis on the gas-bearing situation of the tight reservoirs in the deep Xujiaweizi Depression，Songliao Basin，diagenetic characters of each tectonic unit were studied．Furthermore，diagenetic stages of clastic rocks in each tectonic unit were divided respectively by using the data of fluid inclusions homogenization temperature，Ro，TAI，Rock-Eval，organic acids，XRD，thin section，SEM，blue epoxy resin-impregnated thin sections．As the results show，the diageneses in the uplift of Xujiaweizi Fault Depression are more intense than those of the depressions in Xujiaweizi Fault Depression at the same depth，because the eroded strata in the uplift are thicker than those of the depressions，the thermal gradients in the uplift is higher than those of the depressions，and the strata in the uplift is younger than those of the depressions．Diageneses control the gas-bearing situation of the tight sandstones and conglomerates very much．The sandstones can produce commercial gas flows in the sub-period B1 of middle diagenetic sage，whereas the conglomerates can produce commercial gas flows until in the period A of late diagenetic stage．