Based on the bubble behaviors observed during experiments of pool boiling critical heat flux in inclined confined spaces,an analytical model of critical heat flux is presented,including four major sub-models:a separated flow model,a stability analysis,a heater surface energy balance and a lift-off criterion. Calculation results of critical heat flux agree well with experiment results of 5mm and 8mm gap sizes both qualitatively and quantitatively. Though calculation results show the varying trend of experiment results of 3 mm gap size qualitatively,to some extent the discrepancies do exist quantitatively. In addition,the calculation results predict well the experimental results of Yang,Kim,Howard and Gribov,but the discrepancies between the calculation results and Guo’s correlation are great.