A kind of dynamic testing soil particle size nuclear analyzer is developed.Detection principle of the analyzer is that the tested samples of soil particle are mixed fully dispersive in barrel and dispersant is joined

137Cs is used to launch γ-rays on samples barrel of certain level depth place

suspending liquid density reduce gradually.The analyzer detect relationship between suspending liquid density ρ and time t

according to the Stokes principle and geotechnical tests standard（GB/T50123-1999）.The particle size and particle gradation can be calculated by microcomputer system analysis and data processing.The results show that the instrument has good stability

high precision and sensitivity and fast response

etc.