Abstract: In order to master calculation of drying rate of tobacco leaves，and to provide technical support for accurate curing，mathematical model of relative water-loss rate of tobacco curing was studied.Thin colloidal capillary porous drying kinetics was investigated，and experimental measured data using 101A-3 electric drying oven with forced convection（Shanghai Experimental Instrument Factor）under condition of temperature 39 ℃，wet ball 32 ℃ and fan gear opened on first gear were analyzed to construct mathematical model.The constructed mathematical model of wet-surface ratio was fi=φ×（1－Hsi）=XiXC×（1－Hsi），and simulation values of model and observation values fitted well and error was small.Mathematical model of relative water-loss rate was F=fi×（1－Asi）×（1－Lsi）×（1－Ksi）×（1-Hsi）×（1-HXi），and simulation values of model and measured values fitted well and error was small by curve graph，t test and correlation coefficient analysis.Model of relative water-loss rate could calculate water loss rate in deceleration stage during tobacco curing，and solve problem of water loss which difficult to calculate in deceleration stage during curing，and provide a new mathematical model to accurate control tobacco curing and calculate water loss rate.