In order to adapt fiber lasers and fiber devices to the application of laser engineering system, an auto-correlator based on the fiber devices is designed. The 11 fiber polarization independent beam splitter, fiber collimator, fiber polarization controller, fiber coupler with different ratios, fiber isolator, and fiber interface spectrometer are used in the system. The influence of fiber polarization effect, polarization requirement of frequency-double crystal, coupling efficiency of fiber collimator on the autocorrelation measurement are analyzed and the corresponding methods of overcoming those defects are introduced. Experimentally the output pulse width of nonlinear polarization rotation mode-locked fiber laser is measured and the auto-correlator is feasible. It is indicated that the fiber auto-correlator has the characteristics of convenient connection with fiber laser systems, simple and light structure and so on.