A multi-plunger coordinated gas lift liquid drainage system and liquid drainage method thereof, the system operates in a reciprocating manner. A large-section liquid column and a gas column within a tubing is divided into multiple units of liquid columns, plungers and gas columns by a plurality of plungers; the units form a series connection, and the plungers in the tubing move up and down respectively to transfer the liquid load cooperatively. A liquid is drained from a wellbore step by step, and the pressure formed by a small section of liquid column disappears each time a small section of liquid column is drained. The pressure of each stage of gas column thereunder is reduced, and the gas columns are expanded step by step.