Provided are a surface nuclear magnetic resonance system excited by a geoelectric field and a field working method for groundwater detection. A computer is connected to a synchronization module via a transmitter. The transmitter is connected to a first electrode and a second electrode via a transmission line. Receiving coils are symmetrically arranged on two sides of the transmission line. Each of the receivers is mounted with two receiving coils. The computer is connected to a fourth receiver via a first receiver, a second receiver, a third receiver, a sixth receiver and a fifth receiver, and the synchronization module is connected to the first receiver, the second receiver, the third receiver, the fourth receiver, the fifth receiver and the sixth receiver.