Discussing practically and theoretically the tectonogeochemical diagrams given by J. A. Pearce and others to identify basaltoids forming tectonic setting, the paper suggests, the diagrams are mainly the distinquishion diagrams of rock types, and the principle reason why the diagrams can't certainly identify the tectonic setting is that there isn't complete mirror relationship between the tectonic setting and basalt-forming conditions. The diagrams should be used with caution.