Plant biomass allocation pattern reflects the environmental selection to plant and plant adaptation to heterogeneous environment. In this study, the method of standardized major axis estimation was adopted to study the effects of different developmental stages of patch (formation, diffusion, stability and recession) on stem and leaf biomass allocations of Melica przewalskyi in an alpine grassland of Qilian Mountain. The results showed that in the process of patch development, stem biomass accumulation increased firstly then decreased while the change of stem biomass allocation was on the contrary. Both leaf biomass accumulation and biomass allocation increased in stages of patch formation, patch diffusion and patch stability while decreased in the stage of patch recession. Isometric relationship between stem mass and leaf mass was found in patch formation stage, but allometric relationship was found in the other three stages. The growth speed of leaf mass was greater than that of stem mass at patch diffusion and patch stability stages, but the growth speed of stem mass was greater than that of leaf mass in patch recession stage. Overall, this study demonstrates the significant effect of disturbance on the growth of M. przewalskyi. Biomass allocation of stems and leaves in M. przewalskyi at different development stages showed that the reduction in leaf mass is faster than that of stem mass with the process of patch development.