The invention discloses an inner wall spraying robot system and an inner wall spraying method. The system comprises a robot and an air cushion transport vehicle, wherein the robot is used for finishing the spraying work; the robot comprises a spray gun, a crank arm, a telescopic arm and a base, which are connected in turn; the sum of freedom degrees of the spray gun, the crank arm, the telescopicarm and the base is not less than 6; and the robot is arranged on the air cushion transport vehicle, the air cushion transport vehicle comprises an air bag positioned at the bottom thereof, and the air bag is used for floating the air cushion transport vehicle so as to coarsely position the system before the system enters a working area. The technical proposal of the invention realizes spraying work for the inner wall of a special-shaped long and narrow pipeline through multi-redundant freedom degree design for the robot, and improves the efficiency of preparation work before the spraying work.