Plane-wave pseudo-potential methods based on density functional theory are employed to investigate the electronic structures, magnetic properties of newly designed DO3-type XO3 (X=Li, Na, K and Rb) compounds. Result shows they are d0 HM ferromagnets with total magnetic moment of 5.00 μB. Importantly, the d0 HM characteristic is originated from the polarization of the p-orbitals of O atoms in these hypothetical compounds. The structure stability in the aspects of cohesion energy and formation energy of these four compounds have been tested. The spin-flip gaps of the four XO3 compounds are quite large (>1.00 eV). Furthermore, the d0 HM behavior can be maintained in a wide range of lattice constants.