A child safety seat and a side wing height and width synchronous adjustment mechanism therefor. The side wing height and width synchronous adjustment mechanism includes a first guide rail extending in the width direction of a child safety seat, a second guide rail extending in the height direction of the child safety seat, a first fitting guide member in sliding-fit with the first guide rail, and a second fitting guide member in sliding-fit with the second guide rail, wherein the first guide rail is arranged on one of a side wing and an adjustor, and the first fitting guide member is arranged on the other one of the side wing and the adjustor; and the second guide rail is arranged on one of a first backrest and the side wing, and the second fitting guide member is arranged on the other one of the first backrest and the side wing.