This study assesses the Arctic sea ice thickness (SIT) from the historical run of the Coupled Model Inter-comparison Project Phase 6 (CMIP6). The SIT reanalysis from the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) product is chosen as the validation reference data. Results show that most models can adequately reproduce the climatological mean, seasonal cycle, and long-term trend of Arctic Ocean SIT during 1979 - 2014, but significant inter-model spread exists. Differences in simulated SIT patterns among the CMIP6 models may be related to model resolution and sea ice model components. By comparing the climatological mean and trend for SIT among all models, we evaluate the Arctic SIT change in different seas during 1979 - 2014. Under the scenario of historical radiative forcing, the Arctic SIT will probably exponentially decay at -18 %/decade and plausibly reach its minimum (equilibrium) of 0.48 m since the 2070s.