A device for quantitatively detecting carbon 14 isotope by a dual-wavelength method, wherein the device comprises: a first laser source, a second laser source, a first laser locking module, a second laser locking module, a sample chamber and a signal detecting module; the first laser source is configured to output a continuous pump light; the second laser source is configured to output a continuous probe light; wherein the pump light and the probe light are mid-infrared laser light with different wavelengths; the first laser locking module is configured to lock the pump light in the optical cavity of the sample chamber; the second laser locking module is configured to lock the probe light in the optical cavity of the sample chamber; the sample chamber at least comprises a cavity length adjusting unit; the cavity length adjusting unit is configured to tune the mode frequency of the optical cavity by adjusting the cavity length of the optical cavity, wherein: the frequency of the pump light, as adjusted by the first laser locking module, is consistent with one of the mode frequencies of the optical cavity and matches with an energy difference between a first energy level E1 and a second energy level E2 of a target isotope molecule, the target isotope molecule being a molecule containing carbon 14 isotope, and the frequency of the probe light, as adjusted by the second laser locking module, is consistent with another one of the mode frequencies of the optical cavity and matches with an energy difference between the second energy level E2 and a third energy level E3 of the target isotope molecule; the signal detecting module is configured to detect the optical cavity output signal of the probe light passing through the optical cavity after the laser frequencies and the energy levels of the target isotope molecule are matched simultaneously. the first laser source is configured to output a continuous pump light; the second laser source is configured to output a continuous probe light; wherein the pump light and the probe light are mid-infrared laser light with different wavelengths; the first laser locking module is configured to lock the pump light in the optical cavity of the sample chamber; the second laser locking module is configured to lock the probe light in the optical cavity of the sample chamber; the sample chamber at least comprises a cavity length adjusting unit; the cavity length adjusting unit is configured to tune the mode frequency of the optical cavity by adjusting the cavity length of the optical cavity, wherein: the frequency of the pump light, as adjusted by the first laser locking module, is consistent with one of the mode frequencies of the optical cavity and matches with an energy difference between a first energy level E1 and a second energy level E2 of a target isotope molecule, the target isotope molecule being a molecule containing carbon 14 isotope, and the frequency of the probe light, as adjusted by the second laser locking module, is consistent with another one of the mode frequencies of the optical cavity and matches with an energy difference between the second energy level E2 and a third energy level E3 of the target isotope molecule; the signal detecting module is configured to detect the optical cavity output signal of the probe light passing through the optical cavity after the laser frequencies and the energy levels of the target isotope molecule are matched simultaneously. the frequency of the pump light, as adjusted by the first laser locking module, is consistent with one of the mode frequencies of the optical cavity and matches with an energy difference between a first energy level E1 and a second energy level E2 of a target isotope molecule, the target isotope molecule being a molecule containing carbon 14 isotope, and the frequency of the probe light, as adjusted by the second laser locking module, is consistent with another one of the mode frequencies of the optical cavity and matches with an energy difference between the second energy level E2 and a third energy level E3 of the target isotope molecule; the signal detecting module is configured to detect the optical cavity output signal of the probe light passing through the optical cavity after the laser frequencies and the energy levels of the target isotope molecule are matched simultaneously.