This paper describes the applicability of an open source code “OpenFOAM” on estimating of sloshing wave crest impact pressure acting on a fixed roof of cylindrical tank. Based on the computed results, slosh-induced pressure loads and distribution on the tank roof is presented. A series of large scale tests, which are conducted on the “E-defence” shaking table, has been analyzed. In the shaking table tests, partially water-filled cylindrical tank (diameter/height:3m, water depth:2.3m/1.9m) with the flat fixed roof was subjected to a sinusoidal excitation at the first sloshing resonant frequency. The computer code well simulated the observed waveform with a sharp pressure peak at the time of liquid impact on the tank roof, including appearance of negative pressures in the post impact period, with sufficient accuracy. As for the liquid impact zone of the tank roof, the numerical results indicated good agreement with the observed ones. Consequently, the computer code was capable of predicting the complex nonlinear sloshing behavior with the collision of the liquid surface against the tank roof with an acceptable level of accuracy.