The factor that determines whether an eye is double eyelid or single eyelid is the distribution of the levator muscle in the upper eyelid. Double eyelids have a small part of the levator muscle fibers attached to the skin, most of the levator muscle distribution in the eyelid plate, muscle contraction uplift double eyelids; monocleid eyelid levator muscle without muscle fibers distributed to the upper eyelid skin, but all distributed to the upper eyelid plate, muscle contraction – uplift just eyes open monocleid. According to the position and orientation of the eyelid groove in relation to the upper eyelid margin, double eyelids are categorized as parallel, open-fan, and crescent. Generally speaking, the parallel type looks quiet and detailed; the open-fan type looks cheerful and lively; and the crescent type looks compact and restrained. The junction of the upper and lower lids at the base of the nose is the inner canthus, and the junction of the upper and lower lids on the temporal side is the outer canthus. According to the position of the inner and outer canthus when the eyes are open, the eye shape is divided into three types, according to which different types of double eyelids are chosen. Parallel: The inner and outer canthus are at the same height. You can choose either the open-face type or the parallel type for double eyelids. High inner canthus: the inner canthus is higher and the outer canthus is lower. You must choose the open-fan type for double eyelids. Low inner canthus: the inner canthus is low and the outer canthus is high. A parallel or crescent shape can be chosen for double eyelids. No matter what kind of surgical method is adopted, the principle of double eyelid surgery is the same, i.e., on the designed double eyelid blepharoplasty line, the adhesion between the skin and the eyelid is formed, so that the eyelid and a certain width of skin can synchronize the upward and downward movement during the contraction of the levator muscle to artificially form a double eyelid tissue structure.