The paper presents the results of an analysis of observations of an eruptive prominence on the MFS and HSFA2 spectrographs of the Ondřejov Observatory (Astronomical Institute, Czech Republic) in the lines of hydrogen, helium and calcium. After processing the spectra, the integral radiation fluxes in the lines were determined and a theoretical calculation of the physical parameters of the plasma was carried out using a model in the absence of local thermodynamic equilibrium. A comparison of the observed and calculated values showed that the observed radiation fluxes in the lines can be explained in a model of stationary gas radiation taking into account the opacity in the spectral lines. To calculate theoretical fluxes, in some cases it was necessary to introduce radiation from several layers with different temperatures and heights. The calculated radiation fluxes agree with the observed ones with an accuracy of 10%. As a result of the simulation, the main parameters of the prominence plasma were obtained: temperature, concentration, etc. The values of radiation fluxes in the spectral lines indicate the inhomogeneity of the emitting gas, and there may be regions next to each other whose temperatures differ by an order of magnitude.