Abstract: Shale oil resources are rich in Member 1 and 2 of Qingshankou Formation in the Gulong area of Songliao Basin; a breakthrough of strategic importance has been achieved in oil exploration, and preliminary achievements have been made in the pilot test of reservoir development, showing a broad prospect for shale oil exploration and development. Gulong shale oil is a typical primary reservoir in source strata, characterized with source-reservoir assemblage; it is obviously different from tight oil, sandwich-type and hybrid depositional shale oil in terms of the reservoiring characteristics such as source-reservoir relationship, migration features, accumulation dynamics and boundary conditions, as well as the seepage characteristics involving the phase change mechanism of fluid phase behavior and the staged transportation mechanism of the micro-nano fracture-pore system. In order to effectively achieve the target, a series of key exploration and development technologies with a focus on "box-type reservoir development" has been established, and initial success has been achieved. After hydrocarbon generation of the lamalginite associated with clay minerals in shale oil, the fracture-pore system dominated by organic pores has been formed. Under the joint action of capillary force and viscous force, oil and gas molecules can not migrate, and is preserved in situ under overpressure. Thus, the micro-nano oil-bearing pore aggregates that are distributed in a large scale, relatively independent and have different pressure systems and fluid properties have been formed, thus constituting the primary reservoir in source strata. The key to achieve the development of primary reservoir in the source strata of Gulong shale and maintain stable production of oil well for a long time is to increase the complexity of artificial fractures, and make the oil-bearing pores of different pressure systems gradually reach the fluid start-up pressure and the crude oil occurred in pores flow to the fracture network step by step. Actually, the exploration and development practice has promoted the formation of box division technology with "organic phase + stress step" as the core, the gold target optimization technology with "movable oil content" as the core, and the integrated optimization technology of "one-time well layout, multi-target stacking, three-dimensional interleaving and overall employment", which has achieved obvious application results. The theoretical understanding of oil reservoir formation in the source strata of Gulong shale enriches the traditional petroleum geology theory, which will inevitably lead the development of theories regarding shale oil in source strata in the whole world and push the shale oil revolution to a new height. Furthermore, the large-scale efficient development of Gulong shale oil is of strategic significance for safeguarding the national energy strategy, promoting the construction of comprehensive international energy companies in China and boosting regional economic and social development.