In　this　paper,　the　795-nm　vertical　cavity　surface　emitting　laser　(VCSEL)　with　sub-wavelength　grating　coupled　cavity　is　proposed　and　designed　based　on　the　theory　of　resonant　coupled　cavity,　and　the　mechanism　of　multi-cavity　coupling　linewidth　narrowing　and　influencing　factors　are　analyzed　in　detail　by　using　the　COMSOL　software　finite　element　method.　The　analysis　results　show　that　when　photonic　resonance　takes　place　in　a　multi-coupled　cavity,　the　grating-coupled　cavity　with　reasonable　design　parameters　and　the　multi-coupled　cavity　formed　by　precisely　controlled　lasers　are　phase-matched,　which　greatly　strengthens　the　narrowing　effect　of　the　spectral　linewidth　resonance,　and　a　795-nm　VCSEL　laser　with　high　beam　quality　and　ultra-narrow　linewidth　output　is　obtained,　finally.　Theoretical　results　display　that　the　reflection　spectrum　cold　cavity　linewidth　Delta　lambda　c　of　the　coupling　cavity　with　a　thickness　of　180nm　of　the　spacer　layer　can　reach　7　pm,　which　lays　a　theoretical　foundation　for　achieving　a　kHz-level　spectral　linewidth　output　of　VCSEL　lasers.