Optimizing　the　three-primary-color　perovskite　quantum　dots　(TPC　PQDs)　is　crucial　for　achieving　ultra-wide　color　gamut　displays.　Although　encapsulation　is　an　effective　strategy　to　improve　the　stability　and　optical　performance　of　the　TPC　PQDs,　the　chemicals　or　environment　employed　in　the　coating　procedure　may　attack　the　CsPbX3　PQDs　and　generate　defects,　damage,　and　ligand　loss.　Herein,　a　mild,　facile　and　universal　hexamethylcyclotrisiloxane　(D3)　in　situ　ring　opening　polymerization　strategy　is　successfully　developed　for　efficiently　synthesizing　high-brightness　and　extremely　stable　TPC　CsPbX3@PDMS　(X　=　Cl,　Br,　I)　nanospheres,　with　particularly　friendlyness　for　fragile　red　and　blue.　The　formation　of　Pb　&　horbar;O　bond　between　polydimethylsiloxane　(PDMS)　and　CsPbX3　passivates　the　lattice　defects,　resulting　in　photoluminescence　quantum　yields　(PLQYs)　improvement　of　approximate　to　1.5　times　for　green　and　red,　astonishingly　2　times　for　blue　PQDs.　Also,　PDMS　shell　effectively　blocks　threats　from　the　environment.　Finally,　the　synthesized　CsPbX3@PDMS　nanospheres　are　successfully　applied　in　fabrication　of　the　TPC　light　emitting　diodes　(LEDs)　and　full-color　liquid　crystal　displays　(LCDs),　achieving　impressive　ultra-wide　color　gamuts　of　132%　and　118%　National　Television　Standards　Committee　(NTSC),　respectively.　These　findings　support　the　new　strategy　for　synthesizing　emerging　full-color　perovskite　nanomaterials　and　shows　great　potentieal　for　high　color-rendering　displays.