An investigation on the types of chromosomes and epidemiology of Paragomanni westermanni in five Villages and towns of Huadian city was carried out. The data showed that the infection rate of crayfish, the first intermediate host, was 100% and the infectiosities varied from 99 to 160/per crayfish in the five areas. The genetic patterns of all the cysticercus, ovum and imagoes had been proved to be diploid by morphological and genetic studies. The infection rate of animal final host such as dogs and cats reached as highly as 94.3%, and all the infected animals presented typical pathological changes. Among the total 1008 examined people, the positive rate of skin test of hypersensitivity was 25.1%, and only 0.4% was positive sputum test. Moreover, very few infected people had remarkable clinical expressions, suggesting that the infection of most people was only "transient", or of the larval parasitisim. The results showed that diploid Paragonimus westermanni were not strongly pathogenic to human beings.