I am writing a script to export FBX using MEL,I need to check the “blend shapes” option, but the maya documentation doesn’t have a function for this option,Does anyone know how to set this? Thanks in advance 
Maya documentation on exporting FBX with MEL
It does, and it’s on that docs page you linked, it’s just not very appropriately named:
FBXExportShapes
FBXExportShapes -v [true|false];
FBXExportShapes -q;
Use this function to either exclude or include shape deformations with your FBX file. See Deformed Models in the FBX Export Options for more information.
The link in that section takes you to the user docs about including Blend Shapes and such.
However, iirc, one thing you also have to ensure is that you include any relevant blend shape meshes in your export selection. So even if you had this option turned ON (actually the default according to the docs), then it may still not appear to be working if you didn’t explicitly add the blend shape meshes themselves. I think that’s how it works from memory.
It works.Thank you very much for your professional answer！