Calibration-technology of the star makes use of true pointing of star to calibrate pointing accuracy of electro-optic phototheodolite. The method mostly use of two modes that are time angle and arc-length. Time angle make use of account expressions of true pointing of star through pointing with electricity-optical phototheodolite and compare with true value of theory and finally calculate the error of pointing of electro-optic phototheodolite. The arc-length is new type technology that depends on principle of arc-length changeless to use Polaris with other star in the celestial sphere. This paper introduces the basic principle of the calibration of pointing accuracy of electro optic phototheodolite with the Star arc-length. It analyzes the calibration of precision and point out the factors as attected the precision. It researches the check method in real-time for the range.