Abstract: In the process of the laboratorial dissolved gas analysis (dissolved gas analysis, DGA) on insulating oil, the head-space gas extraction method is a kind of routine oil-degassing method whose accuracy depends mainly on the accuracy of Ostwald coefficient K_i used in the calculation process. In this paper, based on different representation methods of dissolved gas concentration in oil, the effect of atmospheric pressure on the Ostwald coefficient is studied and analyzed by theoretical derivation and experimental exploration, respectively. Then, according to the obtained conclusions, in current related references and technical documents, some critical problems concerning characterization method of dissolved gas concentration in oil of the Ostwald coefficient are analyzed, and correction operations during measuring K_i value are presented. The study and discussion of related issues will be helpful to deepen the understanding and knowledge the dissolution equilibrium and Ostwald coefficient K_i, so as to avoid unnecessary errors in the determination and use of K_i, which may affect the accuracy of the K_i determination results and DGA results. In addition, this paper may also provide references for standards and references revision.