In this paper, we discuss and review the common igneous petrological diagrams, including classification, chemical parameters, and discrimination of tectonic settings. We have reviewed the original petrological meaning of the diagrams and following misunderstanding by others. We also consider different divisions by different people for the same diagrams with same parameters and different interpretations for the same terminology in the diagrams with different parameters. Both correct and incorrect data processing are discussed as well. The discussions and reviews show that complex and multiple systems of the igneous rock must be examined by more diagrams with different parameters in order to better determine the petrological characters. The correct understanding and application of the common igneous petrological diagrams and subsequent suggestions of “the unified platform for the research” may be useful for studying regional petrology.