Corona inception field strength is one of the important parameters for the design of fittings in ±800 kV DC transmission line. So far Peek formula is still the basis for the prediction of corona inception field strength of DC line fittings with large size at high altitude area. Peek formula was obtained by experimental results of electrode with curvature radius less than 50 mm at standard atmospheric pressure. Because the discharge mechanism of the electrode with large curvature radius(larger than 100 mm, hereafter the same)and 3D structure is different, Peek formula is inaccurate for predicting the corona inception field strength for this kind of electrode, especially at high altitude area. In order to predict the corona inception field strength of the fittings with larger curvature radius and non-cylinder structure accuratly, a test platform for HVDC fittings is set up in Kunming high voltage laboratory at 2 100 m altitude. Corona inception voltages are measured for test tubes and rings in the lab. Correction method to Peek formula is proposed firstly for the electrode with larger curvature and 3D structure at high altitude area. This method will become one of the theory evidences for the design of HVDC fittings at 2 km altitude area.