In　this　paper,　the　pendulum　characteristic　of　natural　convection　gas　within　the　3D　spherical　closed　cavity　are　discussed.　By　using　the　finite　element　method,　the　flow　and　temperature　field　caused　by　heat　source　within　the　3D　spherical　closed　cavity　under　different　tilted　conditions　are　calculated.　The　results　are　as　follow:　(1)　Under　buoyancy　effect,　the　direction　of　natural　convection　gas　in　the　cavity　always　stays　in　the　direction　of　the　buoyancy.　(2)　The　isotherm　is　approximately　oval.　The　temperature　field　in　the　direction　of　buoyancy　is　stretched　and　in　the　vertical　direction　of　buoyancy　is　compressed.　The　temperature　gradient　which　is　parallel　to　the　baseline　near　the　heat　source　O　is　equal　with　the　cavity　horizontal.　The　temperature　gradients　are　not　equal　with　the　tilted　angle　of　10°.　The　temperature　gradient　difference　Δδ=4.7　K/mm,　when　the　temperature　of　heat　source　is　473K　and　the　radius　of　the　closed　cavity　is　10mm.　The　temperature　gradient　difference　Δδ=9.5　K/mm　with　the　tilted　angle　of　20°.　(3)　The　difference　of　the　temperature　gradients　on　both　sides　increases　with　the　increase　of　tilted　angle.　There　is　a　linear　relationship　between　the　temperature　gradient　difference　Δδ　and　the　tilted　angle　θ.　©　2018　IEEE.