Along with the continuous extension for application of underbalanced operation and the managed pressure drilling, in order to furtherly carry on the control and the management to these two technologies; according to the risk grade, application category and fluid system, UBO/MPD committee subordinating to International Association of Drilling Contractor classified these two technologies into 6 levels, 3 categories and 5 systems. The paper firstly introduced classification system; analysis and appraisal were separately made on the underbalanced operation and the managed pressure drilling methods about the operation goal, fluid type choice, advantages and disadvantages as well as the applicable scope, so as to provide basis for selecting proper drilling method in construction operation.