Femtosecond laser is a near-infrared light, each laser pulse is emitted for a very short time, which can control the distance of laser travel to the micron level, through the doctor will input the data into the computer, control the laser precise orientation and precise positioning; laser pulse focused into the corneal tissue, the occurrence of light burst thus producing micro-particles to evaporate corneal tissue, produce water and CO2 to separate the cornea. Femtosecond laser has a very short duration of each laser pulse, which is set to act only on the cornea and does not penetrate the cornea into the eye, so it will not hurt any tissues inside the eye, making femtosecond laser safer and more accurate. Each person’s corneal curvature, corneal hardness, corneal size, and corneal thickness are different. In traditional laser surgery, the flap is made differently depending on the corneal curvature, corneal hardness, corneal size, and corneal thickness. Different parts of the same corneal flap are not uniform in thickness. If the flap is not uniform, the corneal stromal bed must also be uneven, which will affect the postoperative visual quality to some extent. In addition, because the thickness of the flap is difficult to be fully controlled by the operator (there is a certain error in the thickness of the flap), the thickness of the stromal bed retained after surgery cannot be accurately estimated before surgery, but can only be roughly predicted (unless it is measured intraoperatively), and the safety of the stromal bed may be compromised if it is not thick enough to develop a cone cornea of medical origin after surgery. Femtosecond laser flaps are created by flattening the central cornea at a level, so that the flap is shaped according to the pre-determined thickness and size, and the quality of the flap is not affected by corneal curvature, corneal hardness, corneal size, or corneal thickness. That is, the femtosecond laser does not affect the quality of flap creation due to individual corneal differences. In addition, because of the small error of the femtosecond laser, the surgeon can set the thickness of the flap according to the patient’s corneal condition, and the thickness is completely under the surgeon’s precise control. Therefore, the thickness of the remaining corneal stromal bed can be accurately predicted before surgery, which is more beneficial to the rational design of the surgical plan and ensure the safety of the surgery.