To provide a theoretical basis for crossbreeding, yielding cultivation of Elymus, an experiment was conducted to study mating system of 3 Elymus spp. by pollen-ovule ration (P/O value), outcrossing index and seed setting rate under different pollination methods. The results showed that the pollen-ovule ration (P/O value) was 31.9-396.0, mating system was the facultative autogamy. Outcrossing index ( OCI ) value is 2, was also the facultative autogamy. Seed setting rate showed that 3 Elymus spp. was selfing, out-cross compatible. As a result, mating system of 3 Elymus spp. belong to the facultative autogamy.