The present invention discloses a Fabry-Perot device compensating for an error of full-width-at-half-maximum (FWHM) and a manufacturing method for the device. The Fabry-Perot device mainly consisted of a Fabry-Perot resonant cavity for a light to pass through. The cavity includes a first reflecting surface with a first reflectance for partly reflecting the light, and a second reflecting surface with a second reflectance for partly reflecting the light. In addition, a distance between the first and second reflecting surfaces may be adjusted according to the first and second reflectance, and thereby compensating for the error of FWHM caused by the first and second reflectance.