Abstract: Relative durations of strong ground motions from 109 station records of MS8.0 Wenchuan earthquake are calculated based on 70% and 90% energy duration definition. Attenuation relationships of the durations under different definitions are statistically analyzed for three component records and 90% duration definition is recommended. The relationships in the hanging wall and footwall of earthquake faults are compared and the ratios of vertical duration to horizontal duration are discussed for different areas.