Abstract: Permeability is an important parameter to evaluate the fluid flow ability in reservoirs. Nuclear magnetic resonance (NMR) logging is the main technology to obtain permeability accurately. However, due to the change of pore structure, the traditional NMR permeability model is not suitable for the evaluation of carbonate formation permeability.The permeability evaluation model of carbonate formation is established by introducing geometric characteristic parameters of T2 spectrum. The model is applied to evaluate the Ordovician carbonate rocks in gas reservoirs in Ordos Basin. It is found that the geometric method can obtain the formation permeability more accurately than the original method.