Abstract: An experimental system was designed and constructed to study the effect of plates on flammable gas cloud explosion pressures.The semi-sph erical gas clouds were formed by 0.02?mm polyethylene films.In the spheri cal center was an ignition electrode that met ISO6184 "Explosion Protection System" and NFPA68 "Guide For Venting of Deflagrations".A data-acquisition syste m,with dynamic responding time less than 0.001s,recorded the explosion pressure-time diagran of acetylene-air mixture with stoichiometrical ratio.The initial cloud radii were 50cm and 100cm.The wood plates did not bend under t he explosion pressures.The distances of plates to the centers of gas clouds were 100,150,200,213.5 and 300?cm,respectively.By fitting the experimenta l data,the relationship between the maximum pressures on the plates and the initial radii of gas clouds,the distances to the centers of gas clouds,the incident angles and the coordinate values on plates are obtained.The equation fitting is effective under 99% confidence based on the mean square deviation analysis.