Synopsis: To measure strip velocity accurately between the stands of the hot strip finishing mill is effective in keeping the stable production and improving the strip dimension control accuracy. Two laser doppler velocimeters has been installed at F4 stand exit and F5 stand exit for evaluating their durability and measurement accuracy. These velocimeters have achieved accurate and stable measurement in bad environment with water splash and high temperature at interstand of hot strip finishing mill by implementing the effective countermeasures to environment and improving the digital signal processing. F5 stand mass flow gage is calculated by using the F4 stand exit gage and the strip velocities measured by these velocimeters. The F4 stand exit gage is measured by existing interstand X-ray thickness gage. The evaluation results indicate that the mass flow thickness has been measured within 0.46% accuracy and will be able to apply to the mass flow AGC (Automatic Gage Control) at the hot strip finishing mill.