For　improving　the　flow　capability　of　gas-exchange　system　in　diesel　with　helical　intake　duct,　the　flow　field　in　helical　intake　duct　was　studied　by　using　the　semi-implicit　method　for　the　pressure-linked　equation　(SIMPLE)　solution　and　the　three-dimensional　compressible　viscous　turbulent　flow　model.　The　effects　of　the　duct　inclining　angle　and　position　on　the　characteristic　of　the　flow　field　were　analyzed.　As　the　complexity　of　the　structure　of　helical　intake　duct,　the　effects　of　the　structure　parameters　on　the　intake　system　with　helical　intake　duct　are　quite　complicated.　The　effects　of　the　duct　inclining　angle　and　position　on　the　flow　in　cylinder　are　of　two　way　type.　The　total　pressure　loss　of　helical　intake　duct　mainly　takes　place　in　the　duct.　The　model　and　the　method　are　proved　to　be　correct　by　experiments.