Intelligent rail surveying instrument is made up of a CPU (89C55 type, low power), some chips, highly accurate sensors and a background light dot-matrix liquid crystal display for wide temperature range. Its surveying results are displayed in liquid crystal Chinese characters. The surveying data are checked and stored in EEPROM automatically. It has automatic breakdown display and a noise alarm function. As a general surveying instrument for both the straight line segment and curved line segment of the rails, it is used to survey the inner width of both rails, height difference and length between two fixed points. After many surveying examinations on the spot, it is concluded that the instrument match well its design and function demands.