The invention discloses a graphite substrate based organic transistor temperature sensor and a preparation method thereof. The organic transistor temperature sensor sequentially comprises a graphite substrate, a dielectric layer, an organic semiconductor layer and an electrode from the bottom up, wherein the organic semiconductor layer and the dielectric layer are in lapping joint with the electrode. The organic transistor temperature sensor adopts the graphite with high thermal conductivity and high electrical conductivity as a substrate, a heat conduction layer and a gate, and adopts an organic semiconductor material to serve as the semiconductor layer based on high sensitivity of an organic semiconductor for the temperature, thereby not only simplifying the structure of the device, butalso reducing the thermal resistance in the heat conduction process, and enabling the device to respond directly, quickly and sensitively to temperature changes.