This　paper　investigates　the　thermal　effects　in　fused-tapered　passive　optical　fibers　under　near-infrared　absorption.　The　thermal　effect　is　primarily　caused　by　impurities,　such　as　OH-,　which　absorb　incident　light　and　generate　heat.　Using　the　finite　element　method,　the　volume　changes　during　fiber　tapering　were　simulated,　influencing　power　density　and　thermal　distribution.　The　heat　conduction　equation　and　ray　optics　were　employed　to　analyze　the　thermal　distribution　in　tapered　fibers　and　signal　combiners.　Results　show　that　at　5　kW　power,　the　temperature　peak　for　a　single　fiber　reaches　316.73　degrees　C,　while　for　bundled　fibers,　the　temperature　rises　significantly　as　the　bundle　configuration　increases　from　7　x　1　to　61　x　1,　peaking　at　453.09　degrees　C-an　increase　of　171.6%.　Variations　in　tapering　ratio　and　length　also　notably　affect　the　thermal　behavior.　Increasing　the　tapering　ratio　from　5　to　8　results　in　a　52.5%　temperature　rise,　while　doubling　the　taper　length　from　25　mm　to　50　mm　reduces　the　temperature　peak　by　59.1%.　These　findings　offer　important　insights　for　the　design　and　optimization　of　high-power　optical　fiber　combiners　and　their　heat　dissipation　structures.