Based　on　the　concept　and　mechanism　of　time　base　distortion,　this　paper　focuses　on　a　trust-region　reflection　least　squares　algorithm　for　estimating　time　base　distortion.　The　method　is　to　estimate　the　time　base　distortion　of　oscilloscope　by　using　multi-frequency　and　multi-phase　signals.　In　this　paper,　the　third　harmonic　model　and　the　average　method　of　20　groups　of　4　waveforms　are　used,　and　the　experimental　verification　is　carried　out.　The　results　show　that　the　trust-region　reflection　least　square　method　is　correct　and　effective　to　estimate　the　time　base　distortion.　©　2023　IEEE.