Abstract: Taking the seeds of Fraxinus mandshurica as the material to release the initial dormancy,after two batches of seeds of pre-water absorption and non-pre-water absorption,at 25℃,with different concentrations（0,25%,50%）of PEG treatment different time（3 days,7 days,3 days PEG+4 days H2O environment）and germination under suitable conditions. The changes of seed water content and seed germination performance during different treatments were determined to explore the changes of water content of seeds treated with PEG at different concentrations and the relationship between the water content and seed germination ability. The results showed that:after PEG treatment,the seed water content of seeds was as follows:contrast＞25% PEG＞50% PEG,that was,the lower the PEG concentration,the higher the seed water content. Among them,after PEG treatment,the water content of seeds treated with pre-water decreased,while the water content of seeds without pre-water increased gradually. At the same PEG concentration for the same time,the germination rate of seeds treated with pre-water and non-pre-water was significantly different,that was,whether PEG treatment or pre-water treatment all affected the change law of seed water content and seed germination ability. The seed water was negatively correlated with the seed germination rate. PEG osmotic treatment attenuated the induction of thermal dormancy of F. mandshurica seeds,which was related to seed water status)