The technology disclosed in this invention belongs to both the field of Nuclear Quadrupole Resonance (NQR) and nuclear geomagnetic resonance application. Technically, a nuclear quadrupole resonance detection system and its antenna are provided. The antenna includes two coils to make a gradient antenna wherein they simultaneously receive both the signal from the target region and the external radio frequency interference. Structurally, the first coil is positioned as a regular circular coil, while the second coil is annular and evenly distributed around the first coil peripherally. These coils are on the same plane with equal areas but have opposite winding directions. The systems specific to the disclosed antenna are also included. The configuration of the invented antenna can effectively increase the capability of suppressing environmental electromagnetic radio frequency interference, thereby enhancing the detection of the NQR or geomagnetic resonance signals. Consequently, the signal-to-noise ratio of the system is improved.