In this paper laboratory and field tests are introduced to evaluate the effects of plant mulluscicide “ Lo-wei ” on killing oncomelania Hubei. In the laboratory ， through spraying into a mud tray ， immersing in a flask and hammering to identify the mortality and survival number of molluscicide ， we have observed the effects of different concentration plant molluscicides “ Lo-wei ”． In laboratory test, the oncomelania mortality is 100% when immerged in 4% Lo-wei powder (TDS) with 7.5g/m³ ， 5.0g/m³ and 2.5 g/m³ concentrations for 48 hours, in which the mortality is more than 95% when sprayed with 7.5 g/m³ ， 5.0g/m³ concentrations of the same TDS. For the in-situ test, the mortality is 100% when immerged in 4% TDS with 2.5 g/m³ concentration in 72 hours, while when sprayed, the oncomelania mortality is 90.03% in 360 hours ． Whether immerging and spraying in laboratory test or in situ test, the efficiency of 4% TDS on killing oncomelania Hubei has reached the qualified index.