Plasmonic nanosensors are promising for chip-based refractometric detections, most of which are based on spectroscopic monitoring of surface plasmon resonance. Here, we propose a simple non-spectroscopic refractometric sensing scheme based on a plasmonic interferometer integrating a metallic groove array and a tilted nanoslit. Owing to the interference of the directly transmitted light from the nanoslit and that mediated by the surface plasmon polaritons launched from the groove array, high-contrast intensity fringe can be detected under the illumination of monochromatic light. By inspecting the spatial shift of the interference fringe, the refractive index change of the cover analyte can be derived. In our experiment, the interferometer shows a sensitivity up to 5 × 10³ μm/RIU and a figure of merit as high as 250. This sensor shows great potential for low-cost, portable, and high-throughput sensing applications due to its simple, robust, and non-spectroscopic scheme.