EN
This paper presents measurement results of the synchrotron radiation infrared transmission spectrum through YBCO film on MgO substrate at T=20 K temperature. The film's transmission temperature of the superconducting state is T_{c}=80 K. During formation cycle the maximum intensity wavelength varies from 100 μm to 10 μm. Due to spectrum evolution the detector signal that gives synchrotron radiation sample transmission is related to the sample transmission ability, the sensitivity of the detector and synchrotron radiation spectrum via an integral equation. The best agreement with experiment results is achieved for the Eγ=20 meV energy gap value, which corresponds to 2Eγ/kT_{c}=2.9 at T=20 K.