The invention discloses a sealing washer of a fiber dye vat, which comprises an open annular washer. The annular washer is formed by enclosing along circumferential tracks, the total length of the annular washer is larger than one circumference, the front end and the rear end of the annular washer are overlaid, a stroke groove is arranged at one end, and a limiting screw penetrated and sleeved in the stroke groove is fixed at the other end. The sealing washer of the fiber dye vat effectively prevents fibers from overflowing out of a dye cage, and simultaneously can adjust the diameter size automatically so as to adapt to stress condition of the dye cage in the dyeing process.