To study the effect of moisture content on accumulation and dissipation characteristics of space charge in oil-paper insulation under DC fields, polarization depolarization current measurement system and space charge measurement system are built to measure the conductance of oil-paper insulation with different moisture contents under DC electric field, and the space charge distribution during pressurization and short-circuiting processes. Results show that at 0.91% moisture content, the conductivity has a one-dimensional linear relationship with DC electric field, while under 5.21% moisture content it comes to be a quadratic parabolic relation. Besides, the increase of moisture content raises conductance of oil-paper by several orders of magnitude. With the same moisture content, the rise of applied DC electric field can increase the same-polarity space charge accumulated at the electrode. At 0.91% moisture content, as pressurization lasts, the positive space charge accumulated inside oil-paper increases, and the implantation depth of space charge improves. When under water contents of 5.21 %, homogenous space charges accumulated near the cathode transfer to the interior of oil-paper at pressurization process. Under different water content conditions, the ascent of moisture content during pressurization process obviously increases homogenous space charge and induces charge accumulated at electrodes. As moisture content rises, more heteropolar space charges accumulate in oil-paper near electrodes, while the positive space charge accumulated inside oil-paper decreases. And in short-circuit process, the increase of moisture content accelerates the discharge process of oil-paper and inhibits the occurrence of polarity reversal at electrodes..