This　study　developed　a　size-dependent　model　to　predict　the　flexural　strength　of　3D　printed　engineered　cementitious　composites　(ECC)　beams　with　different　beam　spans.　The　proposed　model　relates　the　flexural　strength　of　printed　ECC　beams　to　beam　spans　based　on　a　stochastic　tensile　constitutive　model　of　ECC,　by　taking　the　size　effect　into　account.　ECC　beams　with　four　spans　(240　mm,　300　mm,　450　mm,　and　1500　mm)　were　printed　and　tested　by　four-point　bending.　The　results　showed　that　the　size-dependent　model　can　predict　the　flexural　strength　with　an　approximate　accuracy　of　90%.　Compared　to　the　size-independent　model,　the　proposed　size-dependent　model　improved　the　prediction　accuracy　by　approximately　27%.　The　force　analysis　of　the　shear　strength　of　interlayers　further　revealed　that　interfacial　bonding　has　a　negligible　impact　on　the　simulated　flexural　strength.　Consequently,　the　developed　size-dependent　model　can　potentially　guide　the　structural　design　of　3D　printed　ECC　beams.