Abstract：Based on 22 well cores , 4000 logging data and initial potential data, sedimentary characteristics and mode of shallow lacustrine fluvial-dominated delta of Putaohua reservoirs in Sanzhao Sag, Songliao Basin were analyzed. It is realized that submerged distributary channel sandbodies as sand body framework of this delta system is abundant, closely and narrow. It is continual than original understanding and it extends to the far underwater, until disappearing into thin sheet sands. Debouch bar sands is not well preserved and is fluvial-dominated. Based on understanding of Sedimentary Background and sedimentary characteristics and sedimentary facies types of Putaohua reservoirs in Sanzhao Sag, Sedimentary mode of shallow lacustrine fluvial-dominated delta is established, and Sedimentary mode of six subfacies is further divided. Shallow lacustrine fluvial-dominated delta outer front is mode of tide-dominated sheet sand; Transition region of inner front and outer front is mode of fluvial-dominated sheet sand; Inner front is mode of fluvial-dominated debouch bar and mode of fluvial-dominated banding; Transition region of front distributary plain is mode of inshore；Delta distributary plain subfacies is mode of fluvial-dominated banding