Ag　nanoparitcles　were　prepared　via　Ultrasound-assisted　Membrane　Reaction(UAMR)　method.　The　key　issue　of　the　method　is　to　control　precisely　the　injection　speed　of　the　reactants　by　pulseless　pump　to　make　the　nanoparticles　of　Ag　with　small　size　and　narrow　size　distribution.　The　size　and　morphology　of　silver　nanoparticles　were　characterized　with　Transmission　Electron　Microscope(TEM)　and　UV-Vis　spectrum.　The　experiment　results　show　that　the　size　of　Ag　nanoparticles　prepared　via　UAMR　method　was　smaller　than　that　via　Ultrasound-assisted　Dropping　Reaction　(UADR)　method.　The　size　of　80%　Ag　nanoparticles　prepared　via　UAMR　was　ranged　from　3　nm　to　5　nm　with　the　mean　particle　size　4.7　nm　and　considerable　narrow　size　distribution.　The　Ag　hydrosol　fabricated　via　UAMR　method　was　very　stable　at　room　temperature,　even　within　three　months.