The invention discloses a vehicle-mounted mechanical arm ball pickup system based on SLAM and a ball pickup method of the ball pickup system. The ball pickup system comprises a visual sub-system, a central processing sub-system, a driving sub-system, a ball catching sub-system and an energy sub-system, wherein the visual sub-system, on the basis of an SLAM technology, is used for constructing a field raster map and acquiring real-time positional information of a robot main body of the ball pickup system; the central processing sub-system is used for covering the raster map so as to find out atarget ball, and is used for planing a ball pickup movement track in accordance with relative positions of the target ball, an obstacle in the visual field and the robot main body and for transmittinga movement command; in addition, the central processing sub-system, as the robot main body reaches a target ball pickup position, is used for sending a ball catching command; the driving sub-system is used for driving the robot main body to move to the target position in accordance with the movement track; the ball catching sub-system is used for implementing a preset ball catching action after the ball catching command is received; the energy sub-system is used for offering power supply to the other sub-systems; and the central sub-system comprises a force control program based on a zero force control method and is used for compensating gravity force and friction force caused by movement in a ball catching process, so that control over ball catching force is achieved.