Abstract: By using a high speed camera, a visual investigation of vapor bubble growth under different system pressures in narrow rectangular channel was performed. The influences of system pressure, bulk subcooling, wall superheat and bulk velocity on bubble growth were analyzed. Bubble growth model which could meet different experimental conditions was established based on the Zuber model. The results show that Ja, Bo, Re and non-dimensional temperature θ can describe the impact of the thermal parameters and flow parameters on bubble growth comprehensively. The exponential coefficients of K and n decrease with increasing system pressure; bubble growth time and maximum diameter decrease with increasing θ. It is proved that the model correlates with the experimental data very well. As the bubble diameters are stochastic intensely under low pressure, the relative errors between the model predicted values and experimental data under low pressure are relatively large.