Abstract: The Barents Sea and Kara Sea are the regions with significant change of Arctic sea ice. Due to the lack of observations of sea ice thickness and sea ice movement velocity, understanding of the spatial and temporal characteristics of sea ice volume variation in the Barents Sea and Kara Sea region is insufficient. The key processes that cause sea ice changes in the region and the response of sea ice to thermodynamic factors are still unclear. Based on reanalysis data and model simulations of sea ice movement velocity and thickness from 1991 to 2019, the contribution of sea ice variation in the Barents Sea and Kara Sea are analyzed. The results show that, compared with external variation of sea ice transport, local contribution of sea ice variation is the key process of the total sea ice volume change in the region. The external contribution of sea ice is mainly caused by the combined effect of increased outward export and decreased inward import of sea ice between the Svalbard Archipelago and the Severnaya Zemlya. For the local variation, the decrease of sea ice volume is mainly caused by the decrease of sea ice thickness in northern Kara Sea, Barents Sea, and southern Kara Sea. Sea ice has significant negative correlations with sea surface temperature and surface air temperature. The areas with high correlation between sea ice and sea surface temperature are located in the areas with rapid warming in sea surface temperature, where are mainly located in the Barents Sea in spring and summer, and expanded to most areas of the Barents Sea and Kara Sea in autumn and winter. The mean correlation coefficient between sea ice and surface air temperature is higher than that with sea surface temperature. The distribution of areas with high correlation is similar to that of areas with larger decrease in sea ice thickness.