Pore pressure within the core of the embankment dams play a decisive role in performance of the earth dams. Although it may be high during the construction stage of the dam, it will be dissipated to a reasonable level as the consolidation process of the core is progressing in the long term. However, if these dams experience heavy earthquakes in short time, the rapid increase of the pore pressure may put the dam at risk in some critical conditions. In this paper the Excess pore pressure development of the Karkheh large embankment dam during the earthquake loading has been investigated. The Karkheh Dam is the largest storage dam in Iran that has been recently constructed in the south-west of the country. This is an earth dam by a mixed clay core. The length of the dam crest is 3030 m and its maximum height at the river section is 127 m. In the analyses carried out in this study, the FLAC-2D was used.