Abstract: Unconventional tight oil reservoirs, a lightspot in the present unconventional oil and gas exploration, have emerged as a significant source of oil supply in the world. The geological research, theoretical promoting, and present significant issues concerning tight oil will supply and prefect geological theory on unconventional hydrocarbon. Currently, the development of geological research on tight oil can be concluded as follows:① Three main formation conditions and six basic characteristics about tight oil as well as the differences between continental tight oil in China and marine tight oil in the USA have been summarized. ② Pore-throat-fracture network in the tight-oil reservoir has been characterized with advanced and high-precision analysis and testing technology, the formation of tight oil being the primary research object. ③ The accumulation mechanism of tight oil has been deeply studied, which includes charge dynamics, the threshold of charging, migration mechanism, accumulating model, etc. Based on the research status about tight oil, this paper puts forward several important questions about tight oil:① Holographic quantitative heterogeneity characterization on the tight oil reservoir at a micro-nano scale and its effect on tight oil migration and accumulation; ② the genesis of source-reservoir configuration and its control on tight oil accumulation and enrichment; ③ the influence factors and transformation conditions of the occurrence of tight oil, and the relative contribution of different kinds of occurrence status and space; ④ the internal relationship between the mixed sedimentary system in saline lacustrine basins and the formation of tight oil; ⑤ a comprehensive study of the tight oil accumulation factors, and the accumulation mechanism and its whole process. The answers of these questions will play a significant role in geological research on tight oil.