In the experiment, we got the luminous image through photographing the needle-plate corona discharge. The gray value and thickness of corona layer was measured by reading luminescence data using photoshop software. The result shows that, corona luminous intensity is relatively uniform after corona. With the discharge voltage increase, a bright and uneven area was created in the tip place. The corona layer luminous which was around the corona layer of the boundary of 5 gray value, was approximately to be a round ball. Luminous intensity slowly decreased when the needlepoint distance got shorter. Then it rapidly decreased, and then slowly decreased. When corona area in different point appeared luminous, its intensity shows approximate linear increase trend with the increase of the voltage. The corona layer thickness rapidly grew, then there would be a stable region, with the increase of voltage, corona layer thickness got development from flat to ascending.