Heat　transfer　enhancement　was　investigated　in　a　coaxial-pipe　heat　exchanger　using　dimples　on　the　inner　tube.　Through　three-dimensional　numerical　simulation,　the　incompressible　fluid　flow　and　heat　transfer　characteristics　in　the　dimpled　tube　were　studied.　This　computational　model　is　built　up　by　RNG　κ-Ε　turbulent　govern　equation　and　SIMPLE　algorithm.　By　this　study,　the　thesis　shows　that　the　geometry　structures　such　as　the　size,　depth　and　the　distributed　density　of　dimples　affect　heat　exchange　performance　of　dimpled　tubes.　When　Reynolds　number　is　low,　the　heat　exchange　efficiency　of　tubes　with　smaller　dimple　is　higher.　When　Reynolds　number　is　high,　the　heat　exchange　efficiency　of　tubes　with　bigger　dimple　is　higher.