The　flow　dynamics　in　rotor-stator　cavity　with　low-radius　pre-swirl　inlet　was　investigated　both　experimentally　and　numerically.　The　effects　of　flow　rate　and　rotation　speed　on　flow　in　the　cavity　were　studied,　and　the　results　show　that　the　rise　of　static　pressure　through　cavity　increased　with　flow　rate　and　rotation　speed.　The　concept　of　effective　angular　momentum　was　introduced,　the　ratio　of　which　to　angular　momentum　at　cavity　inlet　is　defined　as　angular　momentum　coefficient,　and　by　analyzing　the　relative　magnitude　of　angular　momentum　at　inlet　and　work　done　by　disk　torque,　it　is　found　that　the　corrected　turbulent　flow　parameter　and　the　pre-swirl　inlet　Reynolds　number　were　the　two　main　nondimensional　parameters　affecting　angular　momentum　coefficient.　Given　the　geometry　of　pre-swirl　system,　when　the　rotation　speed　changed,　angular　momentum　coefficient　decreased　with　the　increase　of　corrected　turbulent　flow　parameter,　and　when　corrected　turbulent　flow　parameter　was　larger　than　0.0646,　angular　momentum　coefficient　changed　slowly,　and　the　effective　angular　momentum　was　about　70%~90%　of　the　inlet　angular　momentum.　When　the　inlet　velocity　changed,　angular　momentum　coefficient　first　decreased　and　then　increased　with　the　increase　of　corrected　turbulent　flow　parameter.　©　2016,　Journal　of　Propulsion　Technology.　All　right　reserved.