Generally,in an experiment oriented to determine soil water retention characteristics,just one soil sample is used continuously.During the experiment,the soil would not change much in organic mater content,clay mineral type and cation exchange capacity,but would in bulk density because of hydraulic and mechanical pressures in combination.Therefore a hypothesis is put forth that soil water retention characteristic should be a surface consisting of mass water content,pressure head and bulk density instead of a curve of two variables,pressure head and water content.In this study,two models to fit soil three-variable characteristic surfaces of different soils were proposed based on the Brooks-Corey soil water retention curve model.Ad-vantages,disadvantages and application conditions of the two were illuminated.In addition,soil three-variable surfaces measured for packed soil samples through centrifuging and controlling bulk density using paraffin material were used to verify the proposed models.Results show that the hypothesis of three-variable characteristic surface is reasonable.The two proposed models based on the Brooks-Corey power function fit the measured data well with determination coefficients being greater than 0.94.Although Model Ⅰ performed a bit better than Model Ⅱ,the latter Ⅱ seems to be superior in application because it contains two additional parameters with definite physical meaning.The findings of this research could be cited as a new method in verifying the effect of bulk density on soil hydraulic parameters.