The invention discloses a tunable narrow linewidth laser based on an organic and inorganic hybrid waveguide. The laser comprises a planar optical waveguide and a semiconductor optical amplifier. The planar optical waveguide comprises a substrate layer, a lower cladding layer, a waveguide core layer, an upper cladding layer and an electrode layer. The waveguide core layer is divided into an inorganic waveguide core layer area and an organic waveguide core layer area. The inorganic waveguide area comprises an annular reflector, a first biconical mode converter, a straight waveguide core layer, asecond biconical mode converter and a parallel channel single micro-ring filter. The semiconductor optical amplifier is bonded on the straight waveguide core layer. The organic waveguide core layer area comprises an inorganic and organic conical mode converter, a thermo-optical switch array and a waveguide grating filter. The other end of the waveguide grating filter is an output port, heating electrodes are arranged on upper portions of the annular reflector, the parallel channel single micro-ring filter, the thermo-optical switch array and the waveguide grating filter. Advantages of a narrow line width and a wide tuning range are possessed, and an output laser has a high side mode rejection ratio.