A multi-leaf collimator includes two leaf sets disposed opposite to each other, a plurality of drive devices, a U-shaped optoelectronic switching system, and a first processor. Each leaf set includes a plurality of leaves; each leaf is configured to move under driving of the corresponding drive device; one or more U-shaped optoelectronic switches in the U-shaped optoelectronic switching system are disposed at a side of the upper end surface and/or a side of the lower end surface of a leaf; the U-shaped optoelectronic switch includes a U-shaped groove, a transmitter and a receiver; the U-shaped optoelectronic switch system generates pulse signals when the leaf is configured to move in the U-shaped groove; the first processor is configured to process pulse signals output by the U-shaped optoelectronic switch system to obtain a quantized value of the state of motion of a leaf.