To study the effect of degassing on the space charge distribution in the insulation of 525 kV HVDC crosslinked polyethylene (XLPE) cable, sample slices are cut from the outer, middle and inner insulation layers of both the degassed and undegassed XLPE cables. Space charge distributions in the samples are tested based on pulsed electro-acoustic method, the electric field distortion rate and the charge volume density attenuation rate are calculated. The results show that the residual amount of crosslinking byproducts in cable insulations decreases successively from inner to outer layers by degassing time, and the contents of the byproducts keep stable after a 30-day degassing. The degassing process of XLPE cable is considered to be completed when the total content of α-methylstyrene, acetophenone, and cumyl alcohol in the insulation inner layer is less than 3 mg/g and, at the same time the content of cumyl alcohol is less than 2 mg/g. The results of space charge measurement illustrate that the accumulation of heteropolar charges in XLPE samples is closely related to the content of crosslinking byproducts. The heteropolar space charges are mainly caused by the disintegration of the byproducts, and their distribution decreases gradually from the inner layer to the outer layer. Compared with the undegassed XLPE samples, the heteropolar space charges accumulation of the degassed samples decreases dramatically, and the electric field distortion rate and the charge density attenuation rate are significantly reduced.