Abstract: Hailaer Basin is an oil-bearing faulted basin in the east of China, where the Lower Cretaceous Nantun Formation is the main oil-generating and oil-bearing strata. After more than 60 years of oil and gas exploration, conventional oil reservoirs developed in the high structural parts of the two main oil-rich depressions, i.e., Wuerxun and Beier sags, have been completely explored, the widely developed tight oil reservoir in slope zone and trough area will become an important replacement field for increasing reserves on a large scale. In recent years, based on the detailed study of source rock, deposition and reservoir conditions, the researchers have achieved a systematic understanding of the hydrocarbon accumulation conditions and modes of Nantun Formation tight reservoir in Wuerxun-Beier sags. The results show that the source rocks of Nantun Formation are mainly developed in the middle and lower part of Member 1 of Nantun Formation. With the rising and falling of lake level, the fan-delta front deposition continuously developed towards the lake basin center, braided river delta front deposition, and lacustrine fan deposition formed by collapse can provide sufficient sand bodies for oil accumulation in the tight oil reservoir. It is further confirmed the distribution of tight oil reservoirs in Nantun Formation is controlled by coupling the effective source rock and deposition fan, and the tectonic setting and dominant sand body are decisive factors for the enrichment of tight oil reservoirs in Nantun Formation. According to the source-reservoir configuration, the tight reservoirs in Nantun Formation can be further divided into the source-reservoir integrated type and the upper source with lower reservoir type. In 2023, the oil company initially deployed Well X38-2H for oil testing in the tight source-reservoir integrated reservoir with more favorable accumulation conditions, and obtained the high production industrial oil flow of 23.2 t/d, which confirms that the current geological understanding and engineering technology can realize the effective production of tight oil reservoirs in Hailaer Basin. The exploration potential of eight main hydrocarbon generation sags, such as Wuerxun, Beier, Hongqi and Bayanhushu, is reevaluated to be 3.84×10⁸ t. Bexi subsag and Wunan subsag are selected as the next key zones for tight oil and gas exploration.