The parameterized formulas of isomeric cross-section ratios, including two adjustable parameters for (n,2n), (n,p), (n, α) reactions at 14.5 MeV, have been derived with some approximations based on the Hauser-Feshbach theory. By fitting these formulas to available data, these parameters have been extracted, and the systematics behavior of the isomeric cross-section ratios has been studied. More accurate and reasonable predictions than before were obtained by using these parameters and the systematics formulas.