Soil liquefaction is seen where the water table is high and soil is cohesionless. Especially, it occurs when drainage is not possible or limited. Consequently effective stress decreases as result of increasing pore pressure during shearing. The significant majority of damage of buildings, roads, bridges and dams in earthquakes are due to soil liquefaction. Recently, the importance of soil behavior during the earthquakes has begun to be discussed. In particular, soil liquefaction can cause serious damages to earth-rockfill dams constructed in earthquake prone areas. In 1994-USA, 105 dams were affected within a 75 km radius from center of the Northridge earthquake of 6.7 magnitude. Some of these dams are earthfill and others are rockfill and not all of these dams were in danger of collapse. However, settlement cracks and/or slope movements have been observed. Others did not affected. Besides, many of these dams experienced the San Fernando Earthquake which has a magnitude of 6.5 occurred in the same area. In 1918, the Lower San Fernando Dam having a height of 42 m which was built using "hydraulic fill" technique was heavily damaged. In this study, Lower San Fernando Dam and earthquake loading is modelled using a finite difference program FLAC which contains Finn liquefaction model. At the end of the analysis, damage to the dam section, plastic shear deformations, distribution of pore pressure and deformations are compared with the real case.