The rail-type automatic variable-magnification lens has changed the curved motion mode of traditional lenses, adopting a high-precision and high-efficiency linear guide rail movement system with smaller coefficient of friction. The internal optical grating real-time records the position of the two groups of optical lenses moving up and down, which eliminates the optical effects and various frictions that cannot be avoided in traditional variable-magnification lenses. This greatly improves the optical performance, precision, stability, and service life of the lens.