This paper deals with infuence of the number of impeller vanes and its shape on performance of dredging pump in case of sucking water only and soil-water mixture.
　These characteristics can be expressed by three parameters, that is, a rate of decrease of total head, a rate of increase of shaft horse power and a rate of decrease of efficiency.
　The expressions are as follows,
　where the exponents n and n' are supposed to be greatly dependent on impeller's shape.
　Yet the exponents N' results in 1.0 throughtout the test, while the exponent n ranges from 1.0 for other vane to 1.5 for three vane impeller.
　Furthemore, the numerical analysis using Finite Difference Method are carried out for the potential flow of water in the spave between two vanes of impeller, while the photographical analysis of solid particles in them are also conducted.
　Consequently, we found that there is a difference between the behaviour of soil particles and that of waver, and that this difference causes the abrasion of the vane in the impeller.