Fluidized bed polymerization reactor and process for preparing polymer

A fluidized bed polymerization reactor, comprising:

• a column (1), in which a liquid distributor (2) and a gas distributor (8) above the liquid distributor are arranged, wherein liquid reactant fed into a bottom zone in the column under the liquid distributor enters into a reaction zone above the liquid distributor after passing through the liquid distributor, the reaction zone being divided into a first zone (11) under the gas distributor and a second zone (12) above the gas distributor;
• and
• a circulating unit (20) for circulating gas material originated from a top zone of the column into the bottom zone thereof in a form of gas-liquid mixture,
• wherein the fluidized bed polymerization reactor is configured so that the gas-liquid mixture undergoes a gas-liquid separation in the bottom zone, the gas phase portion obtained entering into the gas distributor and then into the second zone while the liquid phase portion obtained entering into the first zone through the liquid distributor, so that the temperature in the first zone is lower than that in the second zone.