Ceramic-based　composites　generally　have　low　fracture　toughness,　and　toughening　these　materials　without　sacrificing　their　hardness　has　been　a　big　challenge.　This　study　presents　an　approach　for　toughening　ceramic-based　composites　by　modulating　the　strain　partition　and　stress　distribution　in　phase-boundary　regions.　A　new　concept　of　homogenizing　the　lattice　strain　to　achieve　high　fracture　toughness　in　ceramic-based　composites　is　proposed　based　on　the　collective　lattice　shear　of　martensitic　phase　transformation.　The　strategy　was　demonstrated　by　ZrO2-containing　WC-Co　ceramic-metal　composites　as　a　prototype.　The　crystal　planes　along　the　WC/ZrO2　martensitic　transforming　phase　boundaries　exhibited　significantly　larger　and　uniform　lattice　strains　compared　with　conventional　dislocation　pile-up　phase　boundaries　with　highly　localized　lattice　strains.　The　homogeneous　strain　and　stress　distributions　across　interfaces　enabled　the　composite　to　have　simultaneously　high　fracture　toughness　and　hardness.　The　＂homogenizing　the　lattice　strain＂　strategy　proposed　in　this　work　is　applicable　to　a　broad　range　of　ceramic-based　composites　to　achieve　superior　comprehensive　mechanical　properties.