In order to make clear the cause of abnormal high pressure in formation, a study is carried out on the probability that uplift of formation can result in abnormal high pressure. The result shows that due to the high ratio of thermal expansion coefficient to compressibility of water, uplift can not cause abnormal high pressure in formation.The abnormal high pressure in oil and gas reservoirs requires a large height of uplift, which is unpractical generally.So the main cause of abnormal high pressures is still the invasion of external liquid into closed formations.