Abstract: The decision tree method is frequently used to make exploration decision at present.But the application of this method in practice is not easy because it always considers the whole process of exploration.The exploration of hydrocarbon resources is step-by-step,and each step has its own targets.Only if hydrocarbon exploration best realizes the targets of each step by the least cost,can the whole process of it obtain the best results by the least cost.In this paper,an exploration decision method aiming at getting the most reserves by the least cost in the exploration stage is suggested.