Abstract: Aimed to the Multipurpose Reflectance spectrometer device(MR) physics requirements, which is that the active area with 200 mm×200 mm, the detection efficiency with more than 50% and the position resolution with better than 2 mm, for China Spallation Neutron Source (CSNS) in Dongguang, China. A ³He two-dimensional multi-wire proportional chamber position sensitive neutron detector has been developed by the Institute of High Energy Physics of the Chinese Academy of Sciences (IHEP, CAS). The high-pressure two-dimensional multiwire proportional chamber neutron detector filled with ³He/C₃H₈(6 atm/2.5 atm) mixture gases and the multiwire technology. Firstly, the detection uniformity was tested using the Am/Be neutron source in IHEP and the uniformity could reach to 95.1%. After assembled at #20 beam station in CSNS, the performance of the detector were studied under the neutron beam. Under the selection neutron beam with 2.8Å by the time of flight (TOF), the two-dimensional position resolution and two-dimensional imaging of the detector were measured. The position resolution is 0.99 mm in the X direction (perpendicular to the direction of the anode wire), 1.36 mm in the Y direction (parallel to the direction of the anode wire) and the two-dimensional imaging is clear to identity. The results show that the detector has a good resolution and two-dimensional imaging capability, and it could meet the physics requirements of Multipurpose Reflectance spectrometer device in CSNS.