The characteristics and causes of the climate change over Northern Hemisphere (NH) and Southern Hemisphere (SH) during the Medieval Warm Period (MWP) are analyzed in this paper, based on the climatic simulation results over the past 1500 years using the Community Earth System Model (CESM). Moreover, the commonality and difference in the variations of temperature and precipitation between the NH and SH are also investigated. Six experiments are compared in this study, including Control experiment (Ctrl), Total solar irradiation experiment (TSI), Volcanic eruptions experiment (Vol), Greenhouse gases experiment (GHGs), Land use and land cover change experiment (LUCC) and All forcings experiment (All). Based on the comparison of simulated results with observation and proxy records, the CESMs performance of simulating MWP is verified. The characteristics of the simulated temperature and precipitation by the CESM show similarity to the observation and reconstructions. The results show that the MWP is a global phenomenon. However, the MWP is not a steady and continuous warm period, and there are peak-valley oscillation in it. The global climate is warm and moist as a whole during the MWP. Both the NH temperature variations and the SH temperature variations are generally consistent with those of the whole globe. During the MWP, the NH warming is more obvious than the SH warming and the temperature anomaly amplitude in the NH is significantly larger than the SH counterpart, because the land area of NH is larger than that of SH, and the SH is mainly covered by ocean. The high heat capacity of the ocean leads to the smaller anomaly amplitude of temperature change in the SH compared to its NH counterpart. Besides, during the MWP, the warming in the high latitudes of the NH and SH is stronger than that in the low latitudes. For the precipitation variations, the global mean precipitation anomaly is basically positive. But unlike the temperature, the amplitude of precipitation anomaly in the NH is almost equal to the SH counterpart. The significant precipitation change area is mainly distributed in the tropics. The main cause of the global and hemispheric temperature change is the total solar radiation during the MWP. Moreover, the volcanic eruption is also an important factor leading to the NH temperature change. In addition, the global precipitation change is caused by both the total solar radiation and the volcanic eruption, and the influence of the total solar radiation is more significant. However, for hemispheric precipitation change, the volcanic eruption is the most important factor for NH and SH precipitation change during the MWP.