The relationships between seed diffusion，plant reproduction，self-renewal and competitive abilities were studied by model derivation and computer simulation. Plant community structure and species diversity were not only affected by seed diffusion ability，but also sensitive to self-renewal ability and seed quantity. Therefore，it is suggested that the non-degraded grassland in the Qilian Mountains should be grazed appropriately to benefit the dynamic balance of the plant community. For degraded and potentially degraded grasslands，summer and autumn grazing should be discontinued，while uninhibited grazing allowed in winter and spring.