Fatigue failure of small bore piping caused by vibration in Nuclear Power Plants is a universally concerned problem, and so the vibration assessment of small bore piping is becoming an important part of the daily work and aging management work of Nuclear Power Plants. Measurement method and corresponding assessment criterion for piping vibration levels are introduced based on ASME OM-3 and EDF experience respectively. Based on the effective velocity assessment method, the vibration measurement and assessment of 926 small bore pipes of GuangDong DaYa Bay Nuclear Power Plant were performed. The analysis of peak velocities and effective velocities indicates that effective velocity is a better parameter representing steady-state vibration levels for small bore piping. At the same time, the calculation for the allowable effective velocity of the pipes indicates that the screening value of 12mm/s (effective velocity) may be not conservative for some of the small bore pipes. Dynamic stress analysis and coresponding monitoring and inspecting program are performed to prevent vibrational fatigue or failure occurring.