A method used to yield irradiation product with minimal impurity for the solid target for gallium (Ga)-68/germanium (Ge)-68 generator mainly consists of the procedures: first calculate the thickness d for the electroplated gallium (Ga)-69 on the solid target; and then through a graph of decay curves including 69Ga(p, 2n) 68Ge target thickness and incident energy with 5 different incident energy doses, derive the corresponding irradiation energy dose Yi for each group after decay; and through the graph including 69Ga(p,2n)68Ge incident energy and reaction cross-sectional area, derive the nuclear reaction cross-sectional area for each group for germanium(Ge)-68, gallium (Ga)-68, zinc (Zn)-65 and figure out the mean reaction area (MRA) from the reaction cross-sectional area of each group; and select the maximum germanium(Ge)-68 MRA value and the minimum gallium (Ga)-68 and zinc (Zn)-65 MRA values; and generate the required default irradiation energy for the MRA of each group.