Abstract: Multidimensional modeling of vertical upward subcooled boiling flow was performed and the local two-phase flow parameters (void fraction and bubble size) were calculated by using the computational fluid dynamics code—CFX4.4, in which lateral interfacial effects based on a three-dimensional two-fluid model were accounted for.A sensitivity analysis of the difference method, interfacial force and bubble-induced turbulence and bubble size was made.The method of using the CFD code for prediction of sub-cooled boiling flow in a pipe was established.The predicted lateral distributions of void fraction showed excellent agreement with the measurements at low void fraction, but somewhat larger difference at higher void fraction in vertical upward sub-cooled boiling flow.The predicted lateral distributions of vapor velocity and bubble diameter were not satisfactory.The results showed that a reasonable bubble diameter model and modeling of bubble coalescence and tearing would be necessary for improving calculation accuracy.