Method for producing polyolefin

A method for producing a polyolefin using a polyolefin production system equipped with a first gas-phase polymerization tank and a second gas-phase polymerization tank connected to the first gas-phase polymerization tank through a transfer pipe, the method comprising the following steps 1 to 3 and satisfying the following requirements 1 and 2:

• Step 1:
• a step of polymerizing an olefin in the first gas-phase polymerization tank to obtain polyolefin-containing particles;
• Step 2:
• a step of transferring the polyolefin-containing particles obtained in the step 1 to the second gas-phase polymerization tank through the transfer pipe;
• wherein a fluidized bed of the polyolefin particles or a spouted bed of the polyolefin particles and having a moving bed part is formed in the second gas-phase polymerization tank;
• and
• Step 3:
• a step of polymerizing an olefin in the presence of the polyolefin-containing particles transferred in the step 2 in the second gas-phase polymerization tank;
• and
• Requirement 1:
• the connection place “a” between the first gas-phase polymerization tank and the transfer pipe is higher than the connection place “b” between the second gas-phase polymerization tank and the transfer pipe, wherein the connection place “b” is at the height of the top of the fluidized bed or higher, or at the height of the top of the moving bed part in the spouted bed or higher;
• and
• Requirement 2:
• when P1 represents the pressure in the first gas-phase polymerization tank and P2 represents the pressure in the second gas-phase polymerization tank, 130 kPa≥P1P2>0 is satisfied.