The　viscous　dissipation　effect　induced　by　the　fluid　flow　in　microtubes　was　studied　from　the　aspects　of　theoretical　analysis,　numerical　simulation　and　experiments.　Distilled　water　was　used　as　working　fluid　and　it　flowed　through　smooth　quartz　microtubes　with　inner　diameter　25μm　and　50μm,　Infrared　imaging　technology　was　used　to　obtain　the　surface　temperature　distribution　of　microtube　wall.　Using　SIMPLEC　algorithm,　the　viscous　dissipation　effect　was　simulated　numerically　and　the　relationship　between　Re　and　the　temperature　rise　was　yielded.　Results　of　the　experiment　agree　well　with　those　of　numerical　simulation,　which　indicates　that　ignoring　the　viscous　dissipation　effect　could　ultimately　affect　friction　measurements　and　Re　for　flow　in　microtubes.