Optical system performance is easily affected by variable surrounding conditions, including the precision optical system, as its performance is changed with flow field in the air or surrounding water. The air content of water vapor, carbon dioxide concentration, and dry air has a ratio that will affect the air refractive index. Water is another material of general optical systems, affected by surrounding conditions as well. Lithography and the microscope lens are commonly used for contact with water, with their refractive nature, changed by the pressure and density in the flow field. In addition, temperature and light wavelength are two important parameters of the air and water refractive index. This study calculates fluid field pressure and velocity distribution by Computational Fluid Dynamics (CFD) software, and then transfers it to air and water refractive index differences in the optical system. We also evaluate Optical Path Difference (OPD) with fluid field changes, which can improve optical design and system alignment progress by avoiding surrounding condition changes.