Abstract: For the sake of accurately estimating linewidth enhancement factor of semiconductor lasers with external cavity,optical feedback self-mixing interferometric technology and gradient-based optimization algorithm were introduced to achieve best data-theoretical fitting.In addition,an iterate formula was improved with alterable steps introduced.Simulation and experiment data were obtained.The accuracy of algorithm was higher and antinoise capability was better.The simulation result showed that the relative standard deviation of linewidth enhancement factor was less than 2.55% when signal-to-noise ratio was 20dB.Experiment data result showed that the relative standard deviation of linewidth enhancement factor was less than 5.1%.