The invention discloses a detection method and a device for persistance toxic substance in a nanometer structure, laser is coupled into optical fiber by an optical maser which is as excitation light source of the toxic substance, and then the optical master enters into the first circulator, the laser is exported from the first circulator and is shone down nano-substrate adhered to the toxic substance, a frequency excursion Raman signal relative to frequency of the laser light source is returned to the first circulator because of that Raman scattering effect is strengthened in the surface and Raman signal light is generated, then signal light which is arrived to the second circulator and pass through a tunable fiber Bragg grating is returned into the second circulator, and is exported intoa light detector from a detecting interface, light intensity of the signal light is measured by the light detector, then the toxic substance which is to be detected is decerned. In the invention, thetunable fiber Bragg grating is adjusted, if the light signal is detected by the light detector, then the frequency of the light signal is obtained by adjusting the state of an adjustment device of thetunable fiber Bragg grating, therefore, the toxic substance which is to be detected can be detected. The invention has advantages of high detection accuracy and easy operation.