Swimming goggles have a frame unit, lenses and buckles assembled on the frame unit, and at least a head strap with a plurality of stop grooves. Each buckle comprises an abutting arm having a stop end, an operating lever being movable transversely and bringing the abutting arm to move, and an offset portion between the abutting arm and the operating lever. When the operating lever moves transversely, the offset portion makes the stop end of the abutting arm move upward or downward to abut or release the stop grooves of the head strap. The swimming goggles adjust length of the head strap easily.