Different types of pattern can reflect the condition that the population using the environmental resources and can reveal population biology content and is its external appearance of the status and viability in the community. Stellera chamaejasmea is a toxic perennial weed which is widely distributed in the northern grassland of China, showing a large spread of diffusion trend. There are some studies on Stellera chamaejasme pattern and the relationship between Stellera chamaejasmea and Stipa krylovii populations, discussing the diffusion model and laws of Stellera chamaejasmea population. However, these studies can not clearly understand the effect and relationship of the different age class within the Stellera chamaejasmea population, and can not reveal the function and position of the different age class in Stellera chamaejasmea population. Therefore, we use Ripley's K function to study the pattern-controlling relationship and spatial association of Stellera chamaejasmea plants. It is critical to revealing the process of the diffusion of cooperation and competition relationships of the Stellera chamaejasmea population in degraded grassland. The experiments were conducted in Auguest,2009, station a 2 m×2 m plot in Kangle grassland (38°47'15.8″ N,99° 43' 35.9″ E) Sunan country Gansu province in the upper reaches of Heihe, China.We recorded every one's specific location, at last, 151 Stellera chamaejasme plants were counted in the plot.In our experiment, five grades were divided by shoot number of Stellera chamaejasme cluster, cluster gradeⅠ(1-10),Ⅱ(11-20), Ⅲ(21-30), Ⅳ(31-40) andⅤ(≥40), among which 126 individual plants were on levelⅠ and accounted for 83.4% of the total; 15 individual plants were on level Ⅱ and accounted for 9.9% of the total; 4 individual plants were on both level Ⅲ and level Ⅳ and accounted for the same of 2.6% of the total; 2 individual plants were on level Ⅴ and accounted for 1.4% of the total. Calculating the measured value and the value of upper and lower envelopes by the Visual Fortran 6.5 based on the coordinate getting by GetData Graph Digitizer 2.22, the plot software was Origin 7.5 and CAD 2004. The results showed that:pattern control from level Ⅲ and Ⅳ to others, the pattern-controlling from Ⅳ level to others is the largest at the degree and scale. Level Ⅰ, Ⅱ and Ⅴ did not produce pattern control to others, the relationship is mainly the negative association and no association among Stellera chamaejasme plants. The relationship shows positive association on 20 cm scale between level Ⅳ and Ⅰ, Ⅱ,Ⅴ. The relationship shows positive association on 0-10cm between level Ⅲ and Ⅰ. Two plants that have similar shape are less likely to develop the pattern-controlling relationship, in particular, to the plants which were at a disadvantage and be under control by other plants. Level Ⅳ plants showed strong pattern-controlling relationship and could protect other individuals, which were important for status and viability in the population.