The X-ray emission of the SOL2013-05-13T02:12 X1.7-GOES-class flare registered by the RHESSI spectrometer was analyzed. Various models of fitting the X-ray spectrum are applied. The following radiation models are considered: a two-temperature hot plasma model, a combination of a thin target model and a single-temperature plasma model, a combination of a bremsstrahlung model of a thick target and quasi-thermal radiation of a single-temperature plasma. Their validity to the spectra for this event is discussed. Plasma parameters are evaluated: emission measures, temperatures and density.