We propose a method for the measurement of laser linewidth by delayed self-heterodyne interferometry with ultra-short optical fiber. This method can measure the laser linewidth by the signal-to-noise ratio characteristics of the self-heterodyne power spectrum and the frequency spacing of the coherent envelope peaks. It can measure the laser linewidth at the kHz level using several meters of fiber. The feasibility and accuracy of this method are proved by theoretical derivation and experimental verification. In contrast to the conventional linewidth measurement method, the proposed method is simpler to implement, does not necessitate a rigorous experimental environment, and has a broad application range, which can be used as a new scheme for measuring laser linewidth.