This paper mainly introduces the two cross-linking polyethylene insulation breakdown failure factors: space charge and water tree. And it further analyzes their mechanisms of initiation and growth. Cross-linking byproducts and current type are the major influence factors of space charge which will result in serious electric field distortion in the sample and to cause breakdown of insulation. Water tree is mainly influenced by cross-linking technology, impurities and temperature. Finally, this paper summarizes several influence factors and puts forward some improvement methods such as improving the crystallinity of materials, refining the spherulite size, homogenizing crystal, reducing the defects of cross-linked polyethylene.