Abstarct: The purpose of the magnetic survey is to investigate geological structures and subsurface bodies using magnetic anomalies due to the material in the earth’s crust at an area. Downward continuation filter is a method that use in potential field for data processing and interpretation. This method improves short wavelengths and removes long wavelengths resulting from anomalies caused by subsurface bodies. But because of the nature of the method, its application causes the noise and instability of the results to intensify more deeply than the depth of the underlying objects. To eliminate this instability, the normalized full gradient method is used. Using this method, you can determine the horizontal position and deep expansion of sub-surface objects. The most important parameter in this method is to determine the optimal number of harmonic to calculate the Fourier coefficients, which is improved in the enhanced normalized full gradient as a semi-automatic method. In this study, using the enhanced normalized full gradient method, the optimum of harmonic number is determined for estimating the depth and shape of anomalies. Also, the results of this method are compared with the maximum relative values of Normalized full gradient of magnetic data. To achieve this goal, the first some codes have written in the MATLAB software, then these methods were applied to a few magnetic data obtained from the artificial or synthetic model. The results of the study show that the enhanced normalized full gradient method is more accurate in depth estimation in cases where the magnetic effect due to the existence of an individual anomaly. However, in cases where the anomaly effect is due to the presence of several bodies associated in one area, the method of determining the maximum relative values of Normalized full gradient is useful to choose the optimal number of harmonics. Also, because the optimal number of harmonics in enhanced Normalized full gradient method is smaller, the volume of computation becomes less and the speed increases. These two methods were applied to the magnetic data from Shadan, Jalalabad and Ojatabad areas and the results of them were analyzed.