The enhanced normalized full gradient method is used to investigate and interpret potential field data and to determine the depth of geophysical anomalies, especially magnetic and gravity. One of the most important parameters in determining the depth of body in the normalized full gradient method is choosing the number of harmonic terms. In the enhanced normalized full gradient method, an analytical and graphical method has been used to calculate the optimal number of harmonic terms and estimation the depth of anomaly. In this paper, this method was first applied to the gravity effect of the synthetic model of horizontal cylinder, and then on the magnetic effect of the different profiles from the real data related to Ojatabad ore body iron. The result of this study shows that by using this way, we can determine the range of the number of harmonic terms, surface and deep extension of the anomalous body from potential field anomalies.