In　order　to　confirm　the　sub-wavelength　grating　parameters　and　the　best　position　the　sub-wavelength　grating　being　placed　in　micro-electro-mechanical　system　(MEMS)　wavelength　tunable　VCSEL(top　DBR　surface,　top　DBR　bottom　surface,　inner　cavity)　range　to　realize　stable　polarization　control,　MATLAB　was　used　to　build　MEMS　wavelength　tunable　VCSEL　model,　then　the　reflectivity　of　three　structures＇　top　reflective　mirror　(top　DBR,　grating,　air　gap)　changing　with　the　sub-wavelength　grating　parameters　were　calculated　by　which　the　grating　parameters　range　(high　reflectivity)　making　TE/TM　polarization　of　the　three　structures　stable　could　be　confirmed.　The　reflectivity　difference　for　which　the　high　reflective　corresponding　reflectivity　minus　the　low　reflective　corresponding　reflectivity　in　the　same　grating　parameters　range　can　determine　the　position　where　the　sub-wavelength　grating　is　placed　to　realize　the　most　stable　polarizations.　The　results　show　that　the　sub-wavelength　grating　on　the　bottom　surface　of　the　top　DBR　mostly　can　not　control　TM　polarization,　while　not　only　TE　polarization　but　also　TM　polarization　is　most　stable　when　the　grating　is　placed　in　the　inner　cavity.　TE　polarization　threshold　is　less　than　TM　polarization　of　10　cm-1　within　the　grating　parameters　range　to　realize　TE　polarization　stable,　while　TM　polarization　threshold　is　less　than　TE　polarization　of　5　cm-1　within　the　grating　parameters　range　to　realize　TM　polarization　stable.　©　2017,　Science　Press.　All　right　reserved.