The invention discloses a resonant cavity and a thermal insulation laser employing the same. The resonant cavity comprises a first reflection structure and a second reflection structure which are correspondingly arranged, wherein a gain unit is arranged between the first reflection structure and the second reflection structure, a wrapping layer is arranged at an outer side of the gain unit, the gain unit comprises a waveguide structure and a temperature compensation structure, the waveguide structure is used for amplifying a light ray, the temperature compensation structure is used for compensating an optical path and is arranged in a slit of the waveguide structure and/or a side edge of the waveguide structure, and the waveguide structure and the temperature compensation structure are respectively made of a positive temperature coefficient material and a negative temperature coefficient material. In the resonant cavity, the waveguide structure and the temperature compensation structure respectively select the positive temperature coefficient material and the negative temperature coefficient material, and the wavelength of the resonant cavity can be maintained to be stable under different temperatures by employing the negative temperature coefficient material as compensation; and the effective refractive index of the gain unit of the resonant cavity will not change, the optical path is further maintained unchanged, and the output wavelength of the laser will not drift with a temperature.