Different　from　the　traditional　size　model,　this　research　is　based　on　the　phenomenological　phonon　confinement　model　to　analyze　the　size　effect　of　Si　nanocrystals,　considering　phonon　wave　vector　q,　standard　deviation　σ　and　confinement　coefficient　β　and　their　relative　functional　relationship　comprehensively.　The　discussions　focused　on　the　Raman　shift　and　asymmetry　broadening　of　Si　nanocrystals　embedded　in　amorphous　SiC.　The　results　show　that　as　the　size　of　the　Si　nanocrystals　decreased　to　below　Bohr　radius,　the　q　can　change　from　quasi-continuous　form　to　discrete　form　participating　the　scattering,　and　so　this　discrete　q　can　more　accurately　fit　the　Raman　spectral　lines　of　small-sized　Si　nanocrystals.　Standard　deviation　σ　can　further　precisely　adjust　the　asymmetry　of　Raman　peaks,　and　the　smaller　the　size,　the　greater　the　impact.　The　confinement　coefficient　β　involves　the　influence　of　the　limitation　barrier　height　to　the　Raman　shift.　Finally,　the　theoretical　model　was　compared　with　our　experimental　results　and　literature　data.　It　can　be　found　that　the　comprehensive　consideration　of　the　synergistic　effect　of　the　q,　σ　and　β　should　be　conducive　to　evaluating　the　size　effect,　crystal　morphology　and　relative　proportion　of　amorphous　coated　Si　nanocrystals.　Copyright　©　2021,　Northwest　Institute　for　Nonferrous　Metal　Research.　Published　by　Science　Press.　All　rights　reserved.