Abstract: To investigate the infectious state of intermediate host in ever paragonimiasis epidemic areas and observe the affection of common physical factors such as high temperature and freezing and so forth on encysted metacercaria,parasitizing crabs.Crabs were caught by hand or net and ground with grinder to investigate their state infected by encysted metacercaria.The number of caught crabs is 335.The positive infectious ratio is 42%(96/228) among big ones and the average number of encysted metacercaria is more than 2.5 in each infected one.Among 107 small ones,35 encysted metacercaria were found that is each small crab was averagely infected with 0.33 one.Encysted metacercaria are going to denature and die in boiling water in one minute,can survive after being frozen in -20℃ for one hour and die after 3 hours.The conclusion is that the positive ratio of crabs infected with encysted metacercaria is relatively high in the area.Encysted metacercaria are susceptive to heat and can be killed in boiling water immediately.