Abstract: In order to explore the effect of degassing treatment on the insulation properties of XLPE, the effects of different degassing time on the AC tree initiation and growth characteristics of XLPE were studied in this paper. Firstly, XLPE sheet samples with a thickness of 5 mm were prepared by hot pressing and degassed in a vacuum drying oven at 70℃ for 0 d, 1 d, 2 d, 3 d, 4 d and 5 d, respectively. Then, the AC tree initiation and growth experiments and dielectric properties of 6 groups of samples were tested, respectively. Finally, the changes of crosslinking by-products in XLPE with different degassing time were quantitatively characterized by gas chromatography-mass spectrometry, so as to further analyze their effects on the electrical tree initiation and growth characteristics of XLPE. The results show that, under the set experimental conditions, the electrical tree inhibition performance of degassed samples for 2 days is the best. In the process of degasing, the content of pores and byproducts in XLPE jointly will affect the electrical tree initiation and growth characteristics of the material.The more pores in the material will enable the partial discharge easy to occur in the pores, which leads to electrical tree. Acetophenone, as voltage stabilizer, can inhibit the initiation and growth of electrical tree. Therefore, the dynamic changes of content of pores and byproducts with degassing time lead to the highest electrical tree initiation voltage and the lowest average length and width of electrical tree in XLPE samples degassed for 2 days.