Accurate　rotational　speed　measurement　is　a　prerequisite　for　realizing　the　condition　monitoring　and　fault　diagnosis　of　rotating　equipment.　This　study　proposes　a　novel　rotational　speed　measurement　method　based　on　optical　coherent　displacement　measurement.　An　optical　coherence　system　is　used　to　measure　the　relative　depth　of　the　shaft　surface　with　uniformly　etched　micro-indentations　on　the　circumferential　surface.　Fast　Fourier　transform　(FFT)　and　the　Hanning　window　energy　centrobaric　method　(HnWECM)　are　used　to　process　the　collected　photoelectric　signals　to　obtain　depth　information　and　thereby　realize　the　measurement　of　surface　micro-indentations.　During　the　operation,　the　rotational　speed　of　the　shaft　is　obtained　by　calculating　the　ratio　of　the　angular　difference　between　the　relative　depth　of　the　rectangular　pulses　of　the　surface　and　the　time　interval.　The　experimental　validation　of　the　response　is　performed.　The　experimental　results　show　that　in　the　range　of　0　rpm　to　60　rpm,　the　indication　error　is　0.28　%.　Compared　with　the　results　reported　in　existing　literature,　the　proposed　method　offers　advantages　in　terms　of　accuracy,　linearity,　and　repeatability.　©　2024