Abstract: The present invention relates to the technical field of medical devices. Disclosed is an adjustable collimator, which can solve the problem that existing collimators cannot achieve precise therapy in a small irradiation field. The adjustable collimator comprises a controller and two blade sets arranged opposite to each other; the blade sets comprise a plurality of blades, the controller drives the blades to move so as to form a first irradiation field through which a ray can pass; at least one blade in the blade set is a small irradiation field blade, and at least one irradiation field hole is provided on the small irradiation field blade; the controller is further used to drive the small irradiation field blade to move such that the irradiation field hole becomes a second irradiation field through which the ray can pass, wherein the second irradiation field is smaller than the first irradiation field.