Spectrometer/Telescope for Imaging X-rays is one of the instruments on-board the Solar Orbiter mission. It will be launched in 2020 into heliocentric orbit, with perihelion distance ~0.3 AU. The instrument is a Fourier X-ray imager operating within a range of 4-150 keV. The heliocentric orbit of the spacecraft can be highly affected by streams of solar energetic particle. This will affect the instrument operation by distorting obtained spectra and will complicate image reconstruction. Therefore we performed Geant4 simulation of particles interaction with the instrument, assuming realistic scenarios SEP events. We calculated direct detectors hits as well as secondary radiation from instrumental parts. We have found that the latter may highly influence measured X-ray spectra and reconstructed images, and have to be taken into account during data reduction.