This invention relates to a new process for preparation of bisphenol A by condensation of acetone and phenol under the action of modified cationic exchange resin. Said reaction is carried out in a suspension reaction separation tower. Inert gas as upward gas phase is passed through the bottom of tower and enough resin catalyst is filled on every plate in tower, to take the action of suspension and stirring and removal of water formed in reaction. The phenol and acetone are added into tower from its top and side respectively. By this process, a bisphenol A liquid with a concentration of 30 percent may be yielded, the selectivity of bisphenol A may be as high as 95.5 percent and the conversion rate of acetone may also attain 95.8 percent.