As　a　nondestructive　testing　technique,　terahertz　time-domain　spectroscopy　technology　is　commonly　used　to　measure　the　thickness　of　ceramic　coat　in　thermal　barrier　coatings　(TBCs).　However,　the　invisibility　of　ceramic/thermally　grown　oxide　(TGO)　reflective　wave　leads　to　the　measurement　failure　of　natural　growth　TGO　whose　thickness　is　below　10　µm　in　TBCs.　To　detect　and　monitor　TGO　in　the　emergence　stage,　a　time　of　flight　(TOF)　improved　TGO　thickness　measurement　method　is　proposed.　A　simulative　investigation　on　propagation　characteristics　of　terahertz　shows　the　linear　relationship　between　TGO　thickness　and　phase　shift　of　feature　wave.　The　accurate　TOF　increment　could　be　acquired　from　wavelet　soft　threshold　and　cross-correlation　function　with　negative　effect　reduction　of　environmental　noise　and　system　oscillation.　Thus,　the　TGO　thickness　could　be　obtained　efficiently　from　the　TOF　increment　of　the　monitor　area　with　different　heating　times.　The　averaged　error　of　1.61　µm　in　experimental　results　demonstrates　the　highly　accurate　and　robust　measurement　of　the　proposed　method,　making　it　attractive　for　condition　monitoring　and　life　prediction　of　TBCs.　[Figure　not　available:　see　fulltext.].　©　2022,　Higher　Education　Press.