The present invention discloses a planar surface plasmon resonance detector, wherein a periodic metallic grating structure is arranged on a common glass substrate to replace prisms and generate surface plasmon resonance. The shift of the wavelength or incident angle for surface plasmon resonance is used to detect biochemical molecules. Further, a low-cost white light-emitting diode replaces laser to function as a light source. Via the metallic grating structure and the white light-emitting diode, the present invention can facilitate a low-cost, compact and portable planar surface plasmon resonance detector and popularize the planar surface plasmon resonance detector.