Hydra robusta and H.vulgaris were cut transversely in the sub-hypostome region and the basal portion of two hydranth were grafted together. Three kinds of monster hydras, totally 78 individuals were found after 280 days continuous observation, it was shown that: 1 monster and its asexual reproduction offspring contained 2 kinds of falcate nematocyst ( H.robusta' s and H.vulgaris' falcate nematocyst); 2 its length could reach 52 mm when it stretched its body; 3 the average period of asexual gemmation was more than 10 days; 4 individuals died after reproducing 3-8 generations; 5 those who had 4, 5 and 6 tentacles consisted of 80%, 10% and 10% the individuals respectively; 6 it had no sexual reproduction; 7 it needed a relatively long time to regenerate after being cut off. When completing regeneration, both its form and development were as the normal one; 8 hyperplastic tissue appeared on the surface of its ectoderm, and went to apoptosis on the scapus, or disintegrated 1-2 days after disengaging form matrix; endoderm's cellular conglomeration frequently disengaged from the body, entering digestive chambers. The phenomena of hyperplasia and apoptosis appeared on the monster hydra from heterograft showed that hydra might have primitive immune system that can identify and exclude heterogenetic tissues.