Abstract: In order to analyze the effect of system pressure on bubble growth in a narrow channel,a visual investigation on bubble growth under different system pressure（0.1-1 MPa） in a vertical rectangular narrow channel with 2 mm gap was carried out using the high speed camera.It was found that the bubble was growing at the nucleate site under 0.1-0.3 MPa system pressure;while it was sliding along the heating wall during growing under higher system pressure（p_s≥0.6 MPa）,and the size was much smaller.The heat transfer on the heating wall is obviously different due to different bubble behavior under different system pressure.After non-dimensionalization of bubble radius and bubble growth time with Laplace number,La,and time factor,ξ,respectively,the dimensionless bubble growth curve fits the power curve very well,and the coefficient k of the power curve decreases with the increasing of the system pressure.