The objective of hydrocarbon traps exploration is hankering for maximum profit. To optimize making decision for the hydrocarbon traps, and in order to enhance the strict risk analysis and the economic beneficial evaluation, according to the optimized theory in the operations research, the paper sets up the optimal combination models of hydrocarbon-traps exploring risk and obtaining geological reserves on the basis of calculating geological reserves reasonably and analyzing risk strictly. It can come true and make active the maximal effectiveness in satisfying special restrained conditions, and make the whole trap explorations achieve equilibrium between risking and incoming. That is to say, firstly, reaching maximal geological reserves of trap combinations in the definite rage of risk, secondly, reaching minimum risk of trap combinations in the definite rage of geological reserves. When this method was applied in the Dongying depression reserve traps, for dependable and apt to operate, it can supply more scientific foundations for the exploration decision about hydrocarbon traps.