Based on the clarity of the tight oil concept and connotation, the authors proposed ten key indices to evaluate the tight oil. Tight oil reservoirs can be generally divided into 3 different types based on porosity and permeability, while the tight oil itself can be also classified into 3 types depending on the genetic relationship of a close contact between tight reservoirs and source rocks. To expect the tight oil prospect in China, the authors preliminary forecast that the tight oil geological resources in China are about (106.7~111.5) ×10⁸t. Combined with the analysis of future prospects of petroleum development, the authors come to a conclusion that the tight oil in China should be a realistic replacement resource of the conventional oil.