Transition metal compounds with partially filled 3d electron shells exhibit a variety of physical and chemical properties. They are widely used in sensors, magnetic memory, photoelectronic devices, photocatalysis, and electrochemistry. Therefore, determining and understanding their electronic structure is extremely important. The quantitative analysis of soft X-ray absorption spectroscopy depends on theoretical calculation method for the full multiplet based on crystal field theory and hybridization theory. By incorporating these elements, full multiplet theory can provide an accurate model of the fine electronic structure of transition metals and their ligands. A brief introduction of the basic principles, key parameters, and software relevant to soft X-ray absorption spectroscopy is firstly provided in this review. Subsequently, the applications of theoretical calculation in analyzing the electronic structures of 3d transition metals are discussed with an emphasis on its application in the field of electrochemistry. Finally, some prospects for future development in this field are proposed.