This study aimed to understand the deterioration mechanisms of epoxy resin pouring insulation for outdoor dry-type reactors under the effect of long-term surface tracking discharge. Epoxy resin insulation boards similar to the main insulation composition of the dry-type reactor were poured as the experimental material. A tracking experimental platform of insulation materials was built using an inclined plate method. The tracking discharge characteristics and surface erosion of the insulation materials were measured and analyzed. The characteristics of partial discharge, erosion, hydrophobicity and surface roughness were measured experimentally. Surface morphology, three-dimensional morphology and Fourier infrared images at different stages during erosion of the epoxy resin insulation material were analyzed. The effect of glass fiber content on the tracking resistance to erosion was characterized. The results show that the tracking process of epoxy resin insulation material experienced initiation, stability, development and outbreak periods. The flashover discharge corresponding to the development period was the main reason for the carbonization of the insulating material. During the tracking process, with a change in surface topography and formation of surface products, the surface roughness of the material generally increased along with the surface roughness which rose fastest during the discharge outbreak period. The changes in the surface morphology and three-dimensional morphology of the epoxy resin material constitute the basis for assessing the condition of the insulation surface and development of the erosion. The discharge capacity of epoxy resin generally shows an exponential increase. Adding 20 wt% of glass fibers that are evenly distributed and have reduced exposure can improve the tracking resistance of epoxy resin insulation materials.