Abstract: Due to the complexity of pore structures and conditions of fluid mobility in media with doubleporosity, it is rather difficult to interpret the formation parameters by means of the slope of the straight-line section of the pressure built-up curves. Based on the study of the mathematical solution of the Balenbrat Equation, the authors have worked out a set of charts of dimensionless pressure build-up curves that may be used in the interpretation of coefficient of fluid "channeling", ratio of coefficient of elastic porous volumes, mobility coefficient of fractures as well as parameters for hydrocarbons reserve etc. Explanations have been given in the paper regarding the making and application of the charts. Examples of the application of the charts in the oil fields at Yihezhuang, Kenli, Binsiqu, Jenqiu and Sichuan are included in the appendices to the paper.