Abstract: The electromagnetic environmental problems caused by corona effect of DC line is the key constraint factor for the design of line structure and wire selection. However, most of the current studies on the influence of altitude on the negative DC corona effect have failed to link the micro-processes of the discharge with the macroscopic characteristics, and the relevant mechanisms and laws are still incomplete. Based on the hydrodynamic model, the effects of altitude on the parameters and microscopic characteristics of corona discharge are analyzed. By using a small corona cage and a high frequency current measurement system, tests were conducted at 7 different altitude points in the range of 20 m~4 320 m, data on the macroscopic characteristic parameters of the discharge, including corona current pulse, radio interference and audible noise level were collected at different altitudes, and the fitted functional relationship of the corona effect which considers the effect of altitude was obtained. The results show that the amplitude and repetition frequency of corona current pulse increase with altitude. The average corona current is proportional to the power function of the wire surface field strength, and the scale coefficient is a piecewise linear function of altitude. Radio interference and audible noise also increase with the increase of altitude, and they both have a power function relationship with the mean corona current, and change with the altitude.