Abstract: With the study of structures of more than 100 technetium compounds, a packing saturation principle is proposed based on the cone packing model and the normalized "Van der Waals" radii, in which the sum of the Solid Angle Factors (SAF) of all coordinating ligands reaches a stable region with an average value 0.97 and a characteristic error of±0.13 (no more than the SAF of one common ligand).It is found that the steric effect due to geometrical factors is quite important and deserves more attention in the design of technetium compounds with predicted structure.