Subtle reservoirs can be classified by identifying difficulty, concealed style and hydrocarbon accumulation dynamics. In dynamic mechanism, they could be classified as 5 models of hydrocarbon accumulation: a) hydrocarbon migrating along available channels by buoyanc, b)hydrocarbon inducting into sand lens reservoirs by capillarity, c) by expansion and expelling of gas in deep basin, d) by molecule adsorption, and e) as natural gas hydrate by molecule combination. For lithologic and/or statigraphic reservoirs in different areas, factors predominating hydrocarbon accumulation are varied with different types of basins, structural settings and sedimentary environments. Research progressing on classification, dominant factors, dynamics systems and models of hydrocarbon accumulation in subtle reservoirs are discussed. Future research direction for accumulation mechanism and rule of subtle reservoirs is also proposed.