The main goal of this paper is to determine the threshold magnitude for earthquakes of the Zagros and Alborz-Azarbayejan seismotectonic provinces by comparing them with various methods. So, in order to determination of the magnitude threshold for earthquake catalog: cumulation historical and instrumental data from global resources (ISC, USGS, EMSC,IRSC), and conversion their magnitude to Mw in order to uniformize the earthquake catalog, and removing the foreshocks and aftershocks by the Gardner and Knopoff method. Then magnitude threshold Calculated by Stepp’ Methode (S), Maximum Curvature (MAXC), Goodness of Fit Test (GFT), and the best combination of MAXC and GFT (Best Combination (BC) for catalog. Finally, introduce a composition method between S and S-BC in order to increase resolution to compute magnitude threshold for earthquake catalog.