Disclosed are a magnetic circuit system for a loudspeaker, and a loudspeaker. The magnetic circuit system for a loudspeaker comprises a magnetically conductive plate (11), a central magnet (12), a central washer (14), a side magnet (13), and a side washer (15). The side washer (15) comprises a washer body (151) and a bent portion (152) continuing from the washer body (151). The washer body (151) is arranged on the surface, away from the magnetically conductive plate (11), of the corresponding side magnet (13). The bent portion (152) is bent towards the magnetically conductive plate (11) from top to bottom via a side face (15a) of the washer body (151). The bent portion (152) and the magnetically conductive plate (11) are fixedly welded together. According to the present invention, by providing the bent portion and fixedly welding the bent portion and the magnetically conductive plate together, the side washer, the magnetically conductive plate, and the side magnet between the side washer and the magnetically conductive plate are effectively prevented from loosening and falling off due to insufficient glue bonding strength, thus achieving the object of improving the connection strength of the magnetic circuit system itself.