Since superconductor can carry carrying direcet current with zero resistance, its application in superconducting equipments such as superconduting cable, fault current limiter (FCL), transformer,supercondducting magnetic storage (SMES),generatot/motor has attactive worldwide interetst, among of which the high-temperature superconducting (HTS) transformer has some adavntageous characteristics, that is, small volume, light weightness, low loss, no fire hazard and environmental pollution as well as low leakage reactance. With a brief description on the basic structure of the HTS transformer, this paper focuses on several key issues in its research and development, including insulation characteristics of liquid nitrogen (LN₂) and gas nitrogen (GN₂), analyzing methods of alternative current (AC) losses of the superconducting windings and designs of current leads and non-metallic cryostat, and thus provides useful reference for resaerch and development of HTS transformer.