Abstract: A drying strain model of Pinus massoniana lumber consisting of wood shrinkage element,spring and damper and improved the traditional slicing method was developed in the paper to analyse the free shrinkage,instant elastic strain,visco-elastic strain and mechano-sorptive strain developed in wood drying.Wood drying shrinkage element introduced in the model may explain the original force of producing drying stress of shrinkage differential of different layers.Visco-elastic strain had the same developed law as an instant elastic strain.Mechano-sorptive strain was produced by the common function between stress and MC.Mechano-sorptive strain produced after the end of timber drying was the summation of mechano-sorptive strain during the drying.A majority of mechano-sorptive strain was produced at the prophase of drying.The time of biggest differential of surface shrinkage reached can be used as the time of judging the alteration of the drying schedule,afterwards the drying schedule can be accelerated.