A　hypercompressor　is　essential　part　of　low　density　polyethylene　production.　Designing　and　manufacturing　hypercompressors　requires　further　research　and　improvement.　Packing　cups　are　crucial　components　in　hypercompressors.　Design　of　interference　fit　of　packing　cups　is　of　great　importance　and　lacks　a　complete　method　in　China.　Interference　fit　is　designed　with　two　purpose　which　includes　to　obtain　compressive　state　for　the　inner　cup　and　to　minimize　the　equivalent　stress　of　overall　packing　cup.　A　simplified　model　of　a　packing　cup　is　built　for　theoretical　analysis　to　determine　interference　fit.　In　theoretical　analysis,　the　inner　cup　can　be　in　compressive　state　when　its　maximum　circumferential　stress　becomes　compressive;　The　maximum　circumferential　stress　of　the　inner　cup　decreases　and　turns　compressive　stress　from　tensile　stress　as　the　interference　fit　increases,　while　the　overall　maximum　equivalent　stress　goes　up　after　decline　with　the　rise　of　interference　fit.　Finite　element　analysis　on　a　packing　cup　without　structure　simplification　has　the　same　conclusion　with　the　theoretical　analysis.　In　theoretical　analysis,　interference　fit　δmin,　that　makes　the　maximum　circumferential　stress　of　inner　cup　turn　compression,　and　δ1,　that　obtains　the　minimum　of　overall　maximum　equivalent　stress,　are　derived.　The　conclusion　is　that　the　design　of　interference　fit　should　be　the　larger　one　between　δminand　δ1.　This　conclusion　can　be　a　reference　for　designing　packing　cups　for　hypercompressors.　©　2016　Journal　of　Mechanical　Engineering.