1. Two diplostomulum are discovered in the eyes of rainbow trout (Salmo irideus) from trout farm in Shanxi Province. One is found in the lens and identified as a new species - Diplostomulum shanxinsis, another one inhabit in the vitreous body and its name is not yet given - D. sp. Morphological characteristics of the larvae, especially for the flame cell system have been carefully studied. 2. The sporocyst and cercaria of Diplostomulum shanxinsis are found in the digestive gland (liver) and the outwall of the intestine of snail (Lymnaea auricularia). 3. Cercaria d. shanxinsis penetrates the skin of the host, then through the route of center nerve system and arrives to location in the lens of eyes. It needs about 80-94 days in rainbow eye to develop into fully mature diplostomulum, but about 33 days in Aristichthys mobilis. 4. A life-table of the cercaria is given. The life span of C.d. shanxinsis is about 32 hours in the water temperature 19-23 ℃, the LD_(50) is 27.3 hours. They have photokinsis and appear to the surface of water. 5. Pathological changes effected by the invasion of C.d. shanxinsis have been observed. 6. The taxonomy of Diplostomulum, host specificity of Diplostomulum shanxinsis and D. sp have been discussed. For the control of diplostomiasis and its epidemic in trout farm are discussed as well.