Abstract: With the world^’s oil and gas industry developing from conventional oil exploration and development to unconventional oil field, the study of unconventional oil exploration is drawing great attention. Unconventional and conventional oil and gas are substantially different in terms of eight aspects – basic conception, subject system, geological study, exploration method, evaluation of ^“sweet-spot zone,^” technological research, development method and production pattern. The geological theories of unconventional and conventional oil and gas are based separately on continuous hydrocarbon accumulation theory and buoyant trap accumulation theory. Unconventional oil and gas has two key characteristics. One is continuous distribution of oil and gas in a large area without obvious boundaries of traps. The other is no stable natural industrial output. The Darcy seepage is not obvious. There are two key parameters – porosity is lower than 10% and pore throat diameter is lower than 1μm or air permeability is lower than 1mD. As for conventional oil and gas, the above-stated characteristics and parameters are apparently different. The porosity usually ranges from 10% to 30% and the permeability is usually higher than 1mD. Unconventional oil evaluation is focused on six geological properties, such as source rock characteristics, lithologic character, physical property, brittleness, petroliferous property, and stress anisotropy. Conventional oil evaluation is focused on source rock, reservoir, cap rock, trap, migration and preservation as well as the optimum coupling relations of these six characteristics. There are eight elements for evaluation of ^“sweet spot zone^” of unconventional oil and gas abundance, of which three key elements are TOC higher than 2%, high porosity (tight oil and gas higher than 10% and shale oil and gas higher 3%) and development of micro-fractures. Evaluation of conventional oil reservoir is focused on core elements of accumulations and matching of time and space, emphasizing high-quality hydrocarbon source kitchen, favorable reservoir body, scale of trap, and effective conducting system. Unconventional oil and gas is obviously different from and closely related to conventional oil and gas. Unconventional oil and gas has something in common with conventional oil and gas, such as in the same oil and gas system and sharing the same hydrocarbon source system, the same primary migration force and the similar oil and gas components. Based on the substantial relations in genesis and distribution, conventional and unconventional oil and gas are in ^“orderly accumulations,^” related to each other in genesis, and symbiotic in time and space, forming a set of unified oil and gas accumulation system. In accordance with the law that conventional and unconventional oil and gas are in ^“orderly accumulations,^” the two different types of oil and gas resources should be taken into account as a whole in the process of exploration and development for harmonious development.