Oil and gas abroad have been discovered mainly in the marine strata, but in China the oil and gas have been discovered mostly in the non-marine strata. The basic reason is the contrary sequence of the strata formation in China. As for the former, the shallow strata are mainly marine facies while for the latter the shallow strata are commonly non-marine facies. A huge amount of oil and gas could migrate up and accumulate into different reservoirs from the deep along great crust fractures. The shallow reservoirs were firstly discovered and explored certainly. Three problems are faced to petroleum exploration of marine origin strata in China: 优Organic carbon content of marine carbonate rocks are too low to be large scales of hydrocarbon source rocks; Some problems of hydrocarbon migration in carbonate rocks has not been well solved yet; 忧Origin of hydrocarbon in the marine reservoir rocks has not been clear. Three models of hydrocarbon generation can be reduced to: crust-sourced organic matter, interaction between the crust and the mantle and Fisher-Tropsch synthesis. If we only rely on the organic generation theory and reject the other models of petroleum generation, the theory and practice in petroleum exploration would be hindered. Most of hydrocarbons were formed by Fisher-Tropsch synthesis in the mantle and the mid-crust or by the interaction between the crust and the mantle so that these hydrocarbons can migrate into the shallow from the deeper strata along large fractures and besides accumulating in the shallow, the hydrocarbon can accumulate in the deeper granites, volcanic rocks and metamorphic rocks and also in deeper marine strata in China and in deeper non-marine strata abroad.