Beginning with the primary principles of isentropic potential vorti-city (IPV), "IPV thought" based on the invertibility principle is introduced in this paper. It includes the typical structure induced both by the isolated upper-air IPV anomalies and surface potential temperature anomalies, and quasi-geostrophic and semi-geostrophic theories on the invertibility principle for time-dependent flow. The "IPV thought" is used to interprete the dynamical characteristics of large scale motions, such as the Rossby waves and shear instabilities and so on. Moreover, the method to work out the IPV maps is given, and the applicable forms and limits of the maps are described. And at the same time the compari-sion between IPV maps and isobaric maps are made.