Abstract: There is a confusion in discrimination diagrams of basalts for determining their tectonic environments. The confusion comes from inaccuracy,multi-variant solution and controversy. A fuzzy-mathematical model is set up by compositely using the diagrams, and a best program for discriminating tectonic environments is verified. The envh-onments for formation of basalts can be distinguished into four types:mid-ocean ridge, volcanic arc, continental rift and intraplate environments. By analysing and calculating data from these tectonic environments with the fuzzy-mathematical model and related computer program, a satisfactory result was obtained in examination of the typical tectonic environments.