Freeze drying is an effective method to protect unearthed water-logged archaeological wooden artifacts after they are impregnated in polyethylene glycol solution.In this paper，the freeze drying experiments of simulated wooden artifact were carried out on a self-made apparatus.The diffusion coefficient of water vapor in the drying part was fitted according to the experimental data.For a slow cooling velocity of 0.4℃·min-1，the diffusion coefficient was 1.13×10-4m2·s-1；for a quick velocity of 2.0℃·min-1，the diffusion coefficient was 5.53×10-5m2·s-1.The result would offer help for the time prediction and control optimization of the freeze drying of archaeological wooden artifacts.