The invention discloses a low magnetic field nuclear magnetic resonance method for nondestructively testing sulfate attack damage of concrete and belongs to the field of erosion damage study of concrete materials. The method specifically comprises the following steps: performing vacuum saturation treatment on concrete at different corrosion ages, performing low magnetic field nuclear magnetic resonance (NMR) detection, and obtaining relaxation characteristics of hydrogen containing fluid in concrete pores and MRI (Magnetic Resonance Imaging) results. By virtue of numerical analysis of T2 spectral distribution and T2 spectral distribution integral area in the relaxation characteristics and image analysis obtained by the MRI results, the initial state of the concrete and the change of the inner microstructure in the sulfate attack process are integrally researched, and the defect (pore and crack) information of the test pieces, comprising porosity, pore structure characteristics and distribution, can be obtained. Based on the method, the erosion damage accumulation and evolution law of the concrete test piece microstructure under the load and sulfate coupling effect can be observed in real time.