For the linewidth measurement of the narrow linewidth laser, the resolution of the traditional spectrometer and the F-P interferometer is obviously insufficient to meet the requirement of linewidth measurement. In the experiment, a test platform was built using a spectrum analyzer based on the delay self-heterodyne method. Opportune parameters of the spectrum analyzer was set to distinguish noise suppression, using 20 km delay optical fiber based on the result of the calculation, 80 MHz acousto-optic frequency shifter(AOM)and 50:50 fiber coupler, achieve the photoelectric conversion by the photodetector.Optimally set the visual bandwidth(RBW), resolution bandwidth(VBW) and the scan range. Without reducing the testing sensitivity, the analyzer will distinguish overlapping signals and do not filter out too much high frequency to be distorted. Lorenz curve fitting was carried to the linewidth power spectrum peaks. Then it is achieved that the linewidth of the tunable wavelength fiber laser (1520-1570 nm) is about 161 kHz. It provides a reference to optimize the spectrum analyzer parameter settings and calibrate the linewidth parameter of the narrow linewidth fiber laser.