The study established an integrated model combining radiative transfer and geometric optical properties in order to simulate multi-spectral reflectance of semi-arid natural grassland.The model introduced a geometrical similarity parameter

which describes the influences of plant crown shape on leaf/branch angle distribution frequencies

fraction of shadowed or illuminated canopy and background

canopy reflectance

and finally scene reflectance.The simulated results agreed with the measured values in the three Leymus chinense grasslands with different degradation degree

and the lower was degradation degree

the better were simulated results.For the moderately degraded grasslands

if plant crown height-to-width ratio（chw） was invariant

when 45°≤solar zenith angle（sza）≤75°

no significant differences occurred in scene reflectance（R） for different plant crown shapes;and when 0°≤sza<45° or 75 °<sza≤90°

there existed significant differences in R between conic plant crown and spherical and cylindrical plant crown

but no significant differences between spherical and cylindrical plant crown in all cases.If chw was changed

the above conclusions were still agreed.