Self-rotating　grinding　is　the　most　widely　used　technology　to　thin　silicon　wafer.　The　roughness　is　an　important　indicator　of　thinning　quality　and　processing　accuracy.　To　get　a　better　grinding　quality,　rigid　control　of　roughness　is　required.　Although　the　models　of　roughness　in　metal　and　ceramic　machining　were　extensively　studied,　mechanism　of　roughness　formation　in　silicon　wafer　self-rotating　grinding　was　not　well　understood.　In　this　article,　starting　from　the　mechanism　of　grinding　grooves　formation,　Rayleigh　probability　density　function　was　used　to　characterize　the　depth　of　grinding　grooves.　By　establishing　a　relationship　between　the　roughness　and　the　depth　of　grooves,　a　theoretical　model　of　roughness　was　developed.　The　overlapping　effect　of　abrasive　grains　and　wheel-workpiece　deflection　were　also　considered　to　improve　the　accuracy　of　the　model.　The　model　could　identify　the　effects　of　processing　parameters,　abrasive　grain　size,　material　properties　and　grinding　mark　geometry　on　roughness　quantitatively.　Verification　experiments　under　seven　grinding　conditions　were　performed　to　validate　the　theoretical　model.　The　experimental　values　agreed　with　the　predictive　values　with　less　than　20%　deviation.　Effects　of　wheel　rotation　speed,　wafer　rotation　speed,　feed　rate　and　wafer　radial　distance　on　roughness　were　discussed　in　detail.