The magneto-optic current and electro-optic voltage sensing technologies were combined into a single phase unit which provides a new solution for combined current and voltage sensing and relaying applications. It senses voltage and current by making utilities of Pockels electro-optic effect of a BGO(Bi 4 Ge 3 O 1 2 ) crystal and Faraday magneto-optic effect of a close-loop flint. The 220kV high voltage is directly applied on the BGO crystal without capacitive dividers. This design permits true optical voltage measurement to be performed for the highest possible accuracy and stability. In the current sensor, a light beam circles around the current carrying conductor. The effect of the location movement of the conductor and external magnetic field are reduced. It has superior advantages of compact size, light weight and better performance compared with conventional current and voltage transformers. Composite bushing consisting of a fiberglass tube support and silicone rubber that is filled with SF 6 gas is employed for HV insulation. Connections between the Combined Optical Transformers in the substation and the metering and protecting unit in the control house are via optical fiber cable. The fundamental principal, system design and test result of this new 220kV Combined Optical Transformer will be introduced in this paper.