With the deep submicron technologies, IR drop and electromigration have become remarkable by decreasing of the power supply voltage. Therefore, power grid optimization becomes important to achieve the stable operation of Large Scale Integration (LSI). However, it requires large computation time. In this paper, we propose a novel power grid simulation technique which can be applied to a large scale power grid. The proposal technique achieves "High speed processing by hardware accelerator" and "Realization of high accuracy computation with fixed point arithmetic". The proposed power grid simulation algorithm achieves 32 times more high speed processing than software processing. The accuracy is proven by experimental comparison with SPICE simulation.