The study of corona discharge current-voltage characteristics (CVCs) in high temperature high pressure (HTHP) gases is an important step in development of compact HTHP electrostatic equipment. The scope of the current work was the study of corona discharge CVCs in HTHP nitrogen. Corona discharge ionizer was installed inside of a HTHP casing. Ionizer included star-shaped high voltage electrodes installed inside of a grounded tube electrode. The grounded electrode could be heated. Tests were carried out at various gas pressure and grounded electrode temperatures. The CVC-direct and CVC-indirect characteristics were measured for positive and negative polarity of applied voltage. For the same values of applied voltage, current for negative corona was higher than for positive one. The increase of gas pressure stabilized corona discharge and increased corona onset voltage. Operation of the ionizer at CVC-indirect ensured stable corona discharge. Corona discharge CVCs have shown hysteresis loop which area depended on gas pressure and temperature.