The invention provides an automatic riveting mechanical arm system and a riveting method. A mechanical arm carrying a rivet receiving mechanism is moved to the position below a rivet supply mechanism,and rivets are conveyed to rivet discharging holes through second rivet channels, and fall into rivet receiving holes aligned to the rivet discharging holes; the mechanical arm carrying a riveting pressure head reaches a riveting position, and a first rivet channel is controlled by a regulating component to communicate with one rivet receiving hole which receives the rivet, so that the rivet enters the first rivet channel, and reaches the side opening upstream position of the pressure head body channel of the riveting pressure head through the first rivet channel; the rivet is pushed to a through hole; a push rod is driven by a driving motor to press downwards, and the rivet is pushed out from the riveting pressure head by the push rod; and one end of the rivet penetrates through the overlapping part, and is deformed under the pressure effect after abutting on a riveting die, so that a lock catch is formed, and plates are riveted. According to the automatic riveting mechanical arm system and the automatic riveting method, automatic conveying and riveting of the rivets can be achieved.