I have had the same problem last week and I have solved in this way:
1.Be sure you have installed OCC 7.3 VC++ 2017 64 bit from here (other OCC versions may not run) https://www.opencascade.com/sites/default/files/private/occt/OCC_7.3.0_r...
2.Follow the procedure from here : http://graphics.ucdenver.edu/5565/installing_vsqt.htm
Don't install Qt 2017 VisualStudio Add-in Installer ,if you want work with QtCreator only
In this way I have successfully runned OCC under Qt
Let me know if this is enough for you