Abstract: Surface Nuclear Magnetic Resonance(SNMR) is the unique and direct geophysical exploration technology for the groundwater information exploration. Recently, this nondestructive detection technique was applied to test for the earth-rockfill dam safety detecting of seepage. Due to the detecting signal of Nuclear Magnetic Resonance(NMR) coming from the hydrogen's proton of groundwater, it can be ensured that NMR response only relates to groundwater information. Therefore, the SNMR is the unique and direct geophysical exploration technology for the groundwater information exploration. Geophysicists taking advantage of SNMR exploring groundwater directly, the saturated face attempts to be detected, and the seepage of some dykes and dams could be identified. And a convenient, efficient and reusable approach is provided for diagnosing seepage path of dykes and dams especially the small dilapidated reservoir dams and embankment where accidentsfrequently happened. With NUMIS^POLY multi-channel Magnetic Resonance Sounding tested for detecting the safety of a certain dam body, the saturated face of a certain dam body is acquired, and the seepage of the dam isassessed for hidden trouble. The results show that the SNMR can provide a new, effective and reliable technology for the seepage hidden trouble detection of dams.