Abstract: A planar optical waveguide device (3) and a temperature measurement system. The system comprises a detection light source (1), a photoelectric detector (2), a planar optical waveguide device (3), and a measurement optical fiber (4). The planar optical waveguide device (3) comprises a substrate (5). The substrate (5) is internally provided with N temperature detection channels (31). Each of the temperature detection channels (31) comprises an incident light path (311), a reflected light path (312), and an emergent light path (313). In the N temperature measurement channels (31) arranged in parallel, a point of intersection is provided between the incident light path (311) of one temperature measurement channel (31) and the reflected light path (312) of at least one of the other temperature measurement channels (31). The detection light source (1) is in communication with the incident light path (311). The photoelectric detector (2) is in communication with the reflected light path (312).