The basic principle of measuring the linewidth enhancement factor (LEF) using optical feedback self-mixing interference (OFSMI) method is introduced. The theoretical errors are analyzed at different parameters, and the optimal measurement conditions and stripe positions are given. Based on the charcteristics of optical feedback self-mixing interfence signal, an automatic measurement algorithm is developed. The algorithm can automatically identify and extract all eigenvalues of optical feedback self-mixing interference signal in one vibrant period, and the accurate estimation linewidth enhancement factor can be obtained by the eigenvalues at the optimal measurement stripe position. The simulative data have verified the effectiveness of automatic measurement algorithm. The experimental results show that the accuracy of measuring paramters is better in processing data, and the relative standard error of linewidth enhancement factor is 3.26% when peak-peak value of self-mixing signal is 1.75 V.