Abstract: By using the combination method of mechanical devices and electronic precision measuring instrument, Huafei CQ61180X300Vario miniature precise lathe, SINO KA-300 optical grating ruler and SDS3-1 data display were organically assembled together. A high-precision digital lineation and measuring instrument of specimen gauge length was developed by design, processing, connecting parts and lineation devices. The device is simple, fast, intuitive, cost-effective,and it has properties of accurate lineation, high precision. Nearly a year, the actual application showed that the device met the relevant standards for lineation of tension specimen gauge, measuring the gauge length after rupture, and determinating the gauge length of fatigue specimen at high temperature.