A structurally stable two-dimensional carbon allotrope of graphene is studied theoretically based on the firstprinciples calculations.This allotrope can be formed by inserting acetylene and diacetylene fragments into β-graphyne.The calculations on structure and electronic energy spectra show that the carbon Kagomé lattice is a structurally stable semimetal with the Dirac cones below the Fermi surface,in contrast to the Dirac points at the Fermi surface in intrinsic graphene.