The topic of this thesis is to improve the ionograms scaling results of the critical frequency of F2 layer (foF2). Comparing the foF2 scaling results between the automatic scaling program by using a fuzzy segmentation and a connectedness algorithm and by human eyes, the absolute values of differences between two scaling results less than 1 MHz are less than 60% for the chosen 2304 ionograms. The improved automatic scaling program filters the echo not belonging to the F layer, and then using the F layer echoes to determine the foF2. The absolute values of differences between two scaling results less than 1 MHz are more than 85%, better than the previous program. This thesis also discusses the accuracy of the scaling results. The 2304 ionograms were obtained by the Dynasonde that was established at Dong-Hwa University in Hualien, Taiwan since 2010.