A single stable frequency and narrow line width external cavity semiconductor laser used in interference measurement is proposed. It is constructed with a semiconductor laser, collimation system, a blaze grating, and current and temperature control systems. The one facet of the semiconductor laser is covered by high transmission film, and the other is covered by high reflection film. The blaze grating is used as external cavity light feedback element to select the mode of the semiconductor laser. The current control system is used to provide drive current to the semiconductor laser, and the drive current is allowed to be adjusted in certain range. The temperature is controlled with double temperature controls to make the temperature of the external cavity stabilized in order of 10-3℃. Thus a single longitudinal mode, narrow spectral line width and stable frequency external cavity semiconductor laser is realized, and its spectral line width is compressed to be less than 1.4 MHz and the output stability (including power and mode) is remarkably improved.