Tight oil and tight gas have been a hot area of petroleum exploration, development and research for the past 20 years. Based on extensive research of literature, the study status of tight reservoir characteristics and geneses, petroleum formation and distribution characteristics in tight reservoirs, and petroleum migration and accumulation mechanism in tight reservoirs are firstly summarized in this article. Secondly, the main features of domestic and international tight oil and gas accumulation researches are analyzed. At last, the article point out that the key scientific issue of tight oil and gas pool formation is petroleum injection, migration and accumulation in micro-nano pore network systems, which refers to petroleum injection mechanism from source rocks to tight reservoirs, petroleum migration and percolation mechanism in micro-nano pore network systems and petroleum occurrence and accumulation (detention) mechanism in micro-nano pore network systems. Investigation on tight reservoir oil and gas accumulation mechanism should pay attention to three key scientific problems.