Abstract: By means of artificial field_cage expriments, both intra_ and interspecific competition among the adults of three common, mixed grass_feeding grasshoppers, Sphingonotus ningsianus Zheng et Gow, Compsorhipis davidiana (Sauss), Pseudotmethis alashanicus B. Bienko on the desert grassland of the east side of Helan mountains in Ningxia was detected. The results of daily capacity for eating, high mortality and low fecundity showed that strong intraspecific compesition among species at higher densities existed. Interspecific competition was weaker than intraspecific competition. The interspecific competition was complex in its effects. The species with large size had higher mortality but without distinctive difference in reproduction from the species of smaller size. The intraspecific competition was mainly effected by food limitation, while the interspecific competition was effected by the factors of food limitation and self_adaptation to the environments.

Key words: Pinus tabulaeformis fores, granite parent material, limestone parent material, total nitrogen, available phosphorus, available potassium.