The tuning characteristics of diode lasers in TDLAS (Tunable Diode Laser Absorption Spectroscopy) technology is one of the factors that restrict the measurement performance of the system. Aiming at the inherent wavelength tuning nonlinearity of current DFB lasers, a tuning nonlinearity calibration method based on polynomial fitting current pre-calibration algorithm was proposed. Firstly,the laser current wavelength measurement system was built, the current wavelength relationship was measured and the linearity was analyzed, and the injection current pre-calibration mathematical model was deduced based on polynomial fitting algorithm. Secondly, the fitting effect of polynomial fitting algorithm was analyzed. By comparing MSE value (mean square error) and convergence characteristics of each order fitting polynomial, quadratic polynomial was selected as calibration functions. Experimental results show that compared with the uncalibrated state, the pre-calibration algorithm based on polynomial fitting current greatly reduces the calibrated MSE value. Among them, the laser tuning nonlinear error analysis was performed on the better second-degree polynomial fitting algorithm. Compared with 15.39% before calibration, it was reduced to 2.27% after calibration, it was verified that the calibration method can greatly improve the linearity of current wavelength tuning of DFB semiconductor lasers.