Solid matrix structure

which has significant effect on its transfer properties

has not been systematically studied.In this paper

steam-exploded rice straw（SERS)and inoculum were used as the solid phase and liquid phase of substrates

the change of water retention

permeability and thermal conductivity of substrate with the variation of its three-phase structure was investigated within the particle size range（6.5—0.4 cm)and moisture content range（60%—85%)which was employed in industry.The results showed that liquid phase dominated the phase structure variation

therefore

a three-phase structural index（TPSI)was proposed based on weighted variation coefficient.Water evaporation rate of substrate showed exponential increase with the rise of TPSI

and obvious fluctuation was accompanied

indicating that there were some other factors influencing the water retention of substrate. The effect of particle size on substrates’ permeability weakened gradually with increase of water content

and its variation with TPSI accorded with Bidoseresp function（R2=0.9025).The thermal property of substrate

such as volumetric specific heat

thermal resistivity and thermal conductivity

varied with the increase of TPSI according to power exponent functions（R2=0.8991

0.9135

0.9053);small fluctuation indicated that the effect of water content was stronger than that of particle size.Statistical analysis also proved that the TPSI can reflect comprehensive influence of moisture content and particle size on substrates’ transfer properties.Therefore

the TPSI can be applied to effectively characterize the effect of substrate structure on its transfer properties.