Coincidence Doppler broadening (CDB) technique has been applied to the study on vacancy-oxygen (V-O) complexes and vacancy-hydrogen (V-H) complexes in Si. In order to avoid the difference in the relative core-electron annihilation rate and the directional anisotropy in electron momentum distribution, the Si ion implanted Si is useful as the standard sample for the defect study. V-O complexes give the broad peak from 10x10(-3) m(0)c(2) to 20x10(-3) m(0)c(2) in the CDB ratio spectrum, while V-H complexes the peak with 8x10(-3) m(0)c(2). Combined with the positron lifetime data, the structures of the defects induced by O and H implantations to Si are discussed.