Abstract: The bubble coalescence in narrow rectangular channel during subcooled boiling was studied by experiment. The channel size was 2 mm×40 mm×700 mm and the experiment parameters were as following: The inlet absolute pressure p_in=0.55 MPa, the inlet subcooling Δt_in=31 ℃, the mass flux G=516 kg/(m²•s) and the average velocity v=0.52 m/s. The high speed camera was used to photograph the bubbles and the speed was set as 5 000 frame per second. The bubble coalescence process was divided into four stages: The approaching stage, the coalescence stage, the adjustment stage and the steady stage. After coalescence, the bubble velocity would increase and then decrease, and finally approach steady. The ellipsoid and sphere bubble shapes would alternate to appear. Along with the shape changing, the angle and the axis length would change also. Finally, a new small bubble may be induced during the coalescence process.