The invention belongs to the technical field of optical fiber sensing, and discloses an all-fiber reflective simultaneous measurement device of nitrate concentration and temperature. The device comprises an upper computer, a spectrograph, a Y type optical fiber, a sensing unit and a light source, the sensing unit is composed of a multimode optical fiber and a single-mode optical fiber, which are cascaded, wherein one end of the multimode optical fiber is connected with the Y type optical fiber, the other end of the multimode optical fiber is coaxially fused with the single-mode optical fiber,an outer surface and end faces of the single-mode optical fiber are completely covered with gold films, and a nitrate sensitive film is plated at the outside of the gold film on the outer surface; andat the outside of the nitrate sensitive film, a temperature sensitive film is plated starting from a fused end to a half of length of the single-mode optical fiber along the axial direction of the single-mode optical fiber. The simultaneous measurement device disclosed by the invention not only has a simple preparation process, a low cost and a stable structure, but also can effectively reduce the influence of the temperature on the measurement accuracy of the nitrate concentration by simultaneously measuring the nitrate concentration and the temperature.