[en] Astronomical observation and theoretical motivations have strongly indicated that most of matter in the Universe is made of cold dark matter. A well-motivated class of dark matter candidate is Weakly Interacting Massive Particles (WIMPs). Neutron and WIMPs can produce nuclear recoils via elastic scattering off ordinary matter in terrestrial detectors to the point where neutron can bring a false positive reading. Of crucial importance to the direct detections of dark matter searches is to identify the neutron background and its influence. In order to measure the flux and spectrum of neutron background in China JinPing Underground Laboratory (CJPL), an efficient Gd-doped liquid scintillator detector which possesses a strong (n-γ) discrimination was developed. This paper reports the design and performance of the detector geometry, the type of liquid scintillators and photomultiplier tubes (PMT) as well as the low radioactivity surrounding materials and the energy calibration and the capability of neutron and gamma discrimination. Am-Be neutron source was used to evaluate the neutron detection efficiency and the result is (6.30 ± 0.30)% above 0.2 MeV equivalent electron energy. (authors)