The invention discloses a displacement measuring system, which is characterized by comprising a light source, an Alvarez lens group, a pinhole and a light detector, wherein the Alvarez lens group is composed of a first Alvarez lens and a second Alvarez lens with complementary surface shapes, the second Alvarez lens moves in a direction perpendicular to an optical axis relative to the first Alvarezlens, adjusting a focal length of the Alvarez lens group through adjusting a moving distance, further controlling light energy of parallel light reaching the pinhole; the pinhole is used for emittingconverged light transmitted through the Alvarez lens group; and the light detector is used for detecting the light energy transmitted through the pinhole. The displacement measuring system provided by the invention has simple structure and can realize high-precision measurement of displacement by combining few devices with an optical knowledge, and the measurement precision can be up to 1.33 nm,which is of great significance to application in the high-precision displacement sensing field.