Cavitation erosion will create shock waves and water jets in turbulent flows. These impact pressures will affect the surface, which will lead to crack propagation and severe material degradation. In this study, we have developed hydrophobic polydimethylsiloxane‐based polyurethanes (Si‐PUx) with hydroxypropyl polydimethylsiloxane (H‐PDMS) and polytetramethylene glycol (PTMG) as mixed soft segments and 2,4‐tolylene diisocyanate, 1,4‐butanediol, triethanolamine as hard segments via a polycondensation reaction and studied its properties. The cavitation wear experiment showed that the cavitation erosion resistance of Si‐PUx coating continuously improved with the increase of H‐PDMS content, while the adhesion force of Si‐PUs reduced with the increasing of H‐PDMS content. The surface of Si‐PUx coating after cavitation test was observed using an optical microscope and three‐dimensional profiler. The cumulative mass loss of Si‐PUx with 12.5 wt % H‐PDMS was only 2.96 mg and the surface showed no obvious holes and cracks after 80 h cavitation. The results showed that cavitation resistance had a correlation with degree of water resistance, hardness, adhesion strength, and dynamic mechanical properties of coating. It seemed that the Si‐PUx coating could withstand a longer period cavitation erosion resistance compared to high strength epoxy, which could be used as protective coating for flow components under water. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47668.