Aimed at solving the problem of adopting the altitude of he suitable system in oil and gas exploration, this paper gives demonstrations and explanations, and points out the incorrectness of the utilization of terrestrial height in place of altitude. The new method for determining normal height or positive height is described. With this method, the role of the gravity data can be brought into full play in oil and gas exploration, and the normal height and gravity anomaly can be jointly determined with very high precision. Thus, the demand of oil and gas exploration can be met.