Abstract: Based on the statistical model theory and available measured isomeric cross section ratio, a systematic formula of isomeric cross section ratio with one parameter for proton induced reactions is developed. This formula is applicable for the mass region 44≤ A ≤197, spin region of isomeric and ground states 0 5≤ J m≤9.5 and 0 5≤ J g≤7 of the residual nucleus, respectively. Fair agreement is obtained between the systematics predictions and measurements. Within the range of nuclides and spins the systematics predictions can provide useful isomeric cross section ratio information where experimental data are large discrepant or not available.