Population's spatial pattern and spatial association are the main forms of plant community's ecological relationship and ecological process on the space pattern, which can reveal the dynamic and stability of population structure and community structure. Stipa krylovii, the zonal vegetation in alpine degraded grassland, has a great significance for understanding reproductive strategies of grassland resources with studies on spatial pattern and spatial association among different size classes of S. krylovii population. Study sites locates in the Ma Changtan grassland (38°47'22.1″-38°52'11″ N, 99°45'11.7″-99°57'41.2″ E) which belongs to the upper reaches of Heihe River in the SuNan country of the north Qilian Mountain. In early August, 2011, we recorded the size structure of S. krylovii population and fine-scale (0-100 cm) spatial pattern and spatial association among different size classes from 2 m×2 m grids (2 cm×2 cm quadrats) in four plots under four kinds of degradation gradients: no degradation, light degradation, moderate degradation and heavy degradation. The measured value and the value of upper and lower envelopes were calculated by the Visual Fortran 6.5 based on the coordinate getting by GetData Graph Digitizer 2.22, the point pattern analysis and Monte Carlo stochastic simulation method were used to quantitatively analyze spatial pattern, the excel software was used to construction, the number of Monte Carlo stochastic simulation was 20 times with the step of 2 cm. The results showed that: (1) Along with the natural pasture degeneration process extension, the population's size structure transformed from stable type to instability. (2) Spatial pattern among different size classes existed different characteristics: spatial pattern of plant size A transformed from random to aggregation at 8-69 cm scales in no degradation and light degradation, as well as plant size B transformed at 24-59 cm scales; under moderate degradation conditions, spatial pattern of plant size A and C showed random and aggregation, plant size B showed random and regular; under heavy degradation conditions, all plant size showed random or regular. (3) Spatial association among different size classes was changed on the different scale and degradation gradient: positive correlation was shown between plant size A and B in no degradation and light degradation, whereas no significant or negative correlation was shown under moderate degradation and heavy degradation conditions; no significant or negative correlation was shown between plant size B and C, meanwhile, the scale of negative correlation increased form 6-22 cm to 5-26 cm; positive correlation and no significant correlation was shown between plant size A and C at different degradation gradient type, meanwhile, the scale of positive correlation increased. The changes of size structure of S. krylovii population, as well as the mutual conversion of intraspecific competition and interspecific competition, which are not only the antecedent conditions affecting scale transformation of spatial pattern and spatial association, but also the critical factors of population's status and function change. It may reflect the adaptive approach of regeneration and reproduction when S. krylovii population in the face of the outside interference.