Abstract: Motive characteristic of sliding bubble is visually observed by wide side and narrow side of the narrow rectangular channel using high speed digital camera.The results show that the bubble departing from the nucleate site slides along the heated surface,the typical sliding bubble phenomenon for narrow rectangular channels is observed in low heat flux,and the sliding bubble shape is spherical,and the upstream contact angle of sliding bubble on the heated surface is almost equal to the downstream contact angle of sliding bubble on the heated surface.The increase of the sliding bubble velocity is quick at the initial moment,and the sliding bubble velocity exceeds the local liquid velocity at some time.As the time increases,the sliding bubble velocity is almost equal.The sliding bubble velocity increases with increasing the bubble diameter.The sliding bubble velocity increases with increasing bulk velocity,and the trend of increasing sliding bubble velocity in large bulk velocity is larger than that in low bulk velocity.