Objective Laser-assisted in situ keratomileusis (LASIK) has been widely used in clinical correction of myopia, and its safety, accuracy and stability have been recognized by doctors and patients. Some researchers thought RSBT=300μm is safe, while others thought 280μm or 250μm is safe. In this paper, the biomechanical properties of cornea were studied by using finite element method and mechanical means. We analyzed the effects of different RSBT in LASIK surgery on the geometric deformation and stress changes of the cornea under different intraocular pressures (IOP), and evaluated its safety to obtain the minimum retention value, which will provide a mechanical reference for clinical surgery practice and medical statistical research. Method The finite element software ABAQUS was used to conduct the modeling of a normal cornea and corneas of different RSBT after surgery. Appropriate loading and boundary conditions were set and then the results about displacement and stress were calculated. Results The results about apical displacement of the anterior corneal surface indicate that the apical displacement of the postoperative cornea (RSBT=250μm) under IOP=20mmHg is the same as that of the normal cornea (RSBT=550μm) under IOP=40mmHg; According to the results about the mean radius of curvature of the anterior and posterior central surface of corneas, RSBT=280μm is in the low risk area of keratoconus, while RSBT=250μm has been in the high-risk area; The results about central tensile stress on the anterior and posterior corneal surface indicate that, at a value between 280μm and 300μm of RSBT, the stress distribution is nearly consistent with that of the normal cornea. According to the study of corneal histology, when RSBT=300μm, the stromal layer of the cornea lost the first 40% of the strongest strength against tissue tension. Conclusions RSBT=250μm is the minimum retention value for LASIK surgery; RSBT=250μm is the high risk value; When RSBT=330~340μm, that is, for most patients, LASIK surgery is safe enough.