We propose a two-dimensional metal grating with rhombus particles on a gold film structure for refractive index sensing due to its perfect absorption at near-infrared wavelength.Via two-dimensional metal grating coupling,the incident light energy is effectively transformed into the surface plasmons which propagate along the upper surface of the gold film and interact with the surrounding environment in a wide range.The plasmonic resonance mechanism of the structure is discussed in detail by theoretical analysis and finite-difference time-domain method.After optimizing the geometrical parameters,the designed structure shows the sensing performance with a refractive index sensitivity of 1006 nm/RIU.More importantly,this plasmonic refractive index sensor achieves an ultra wide refractive index sensing range from 1.0 to 2.4 with a stable sensing performance.The promising simulation results of the structure show that the sensor has a broad application prospect in the field of biology and chemistry.