For better understanding of the air beam assisted in-process optical measurement process to improve system design, a CFD study was conducted. In the CFD study, a two-phase flow model was used to examine the gas-liquid two-phase flow in the measurement region. It was found that the CFD results and the experimental results agree very well with each other, demonstrating the validity of the CFD model in simulating and predicting the gas-liquid two-phase flow for the in-process optical measurement process. A number of key issues, such as fluid domain, boundary condition, CEL, meshing, and calibration, will be presented and discussed. Balancing in use of memory and time cost for better computational accuracy for the CFD study of precision measurement will also be discussed.