Abstarct: Sloshing phenomenon is one of the important phenomenons in the fluid mechanics that it is very applications in planing structural-fluid collection and investigate the phenomenon of sloshing is very important.Among the applications of this problem, we can pointed out LNG gas cylinders, air displacement, displacement of marine and ships, that fluid and free surface have important role in it.fluid forces in the components leads to choosing the material and suitable geometry for the equipment. Because of the phenomenon of sloshing, considerably pressure enter of the tank structure. In a lot of cases, use from baffle for decreasing slosh waves. In this paper we purpose that with experimental investigating of pressure of fluid on the tank walls, with fluid and lateraly moving force and validating results from that with the results from numerical simulating, effect of presence of baffle in this parameter, investigated and determing, optimum height of baffle for minimize pressure on the walls. for this porpose, a partially filled rectangular tank with external laterally moving force source and different frequencies on the tank and different heights of liquid in two kind of baffle and without baffle in different heights investigated. For experimental study we made a experimental setup that in it a rectangular tank filled to certain height from fluid. By a mechanical movitation mechanism adjoin to a source of external power generation and placed under external excitation. Parameters such external frequencies on the tank from source of power generation, sway domain, fluid height on the tank and height of embedded baffle in the tank, chanches for more accurate review. Baffle is mounted in the half and bottom of tank and thickness of baffle is thin. The ratio of baffle height (h_b) to initial liquid height (h) has been changed in the range 0≤h_b⁄h≤1.66. for better analysis, results of experimental fluid sloshing data in the tank with baffle validated with results of numerical simulation that good agreement reported between numerical and experimental results.