The measurement methods of narrow linewidth lasers are reviewed. The basic principle of narrow linewidth laser measurement based on optical heterodyne method is introduced. The testing mechanisms of double-light-beam heterodyne and delayed self-heterodyne methods are described. For the systematic error frequently introduced in delayed zero frequency self-heterodyne method, source modulation and path modulation non-zero frequency self-heterodyne methods have been developed, and these improved methods have their advantages and disadvantages, respectively. Moreover, the new measurement methods of narrow linewidth lasers are summarized. The full spectrum of measurement methods of narrow linewidth lasers is shown, and it is seen that double-light-beam heterodyne and delayed self-heterodyne methods can find superiority for different conditions.