Oxygen in YBaCuO superconductor was partly substituted by Cl- in the forms of CuCl2 and BaCl2．There sults show superconductive phase can be obtained no matter CuCl2 or BaCl2 was used. Cl- coming from CuCl2 ccupies O2 site of 123 phase, while Cl- coming from BaCl2 enters O4 site. The former effects superconductivity dramaticaly and the electrical conductivity of normal state changes from metallic behaviour to semiconductive behaviour. The latter reduces Tc，but Tc keeps larger than 77K and the electrical conductivity of normal state still remains metallic behaviour. All these suggest that the oxygen on the CuO plane (O2) plays an important role in the high Tc superconductivity.