The diode-laser absorption spectroscopy has been tuned with fast speed and wide wavelength range by temperature scanning. The system original data does not suit for traditional processing and operation, therefore the proper data preprocessing is the basis of the follow-up operation. The original data is processed according to the characteristics of temperature tuning signal. The temperature detection noise in wavelength sequence is removed by Savitzky-Golay filter, then cubic spline interpolation is applied to obtain amplitude sequence with fixed wavelength position for follow-up operation. The result sequence, which has both information of amplitude and wavelength as the same starting point and fixed wavelength position, not only has 6 times higher signal-to-noise ratio than that of original signal by multi periods averaging, but also makes the comparison and evaluation between different signals possible. The consistent wavelength resolution ensures the precision of lineshape detection and decreases the frequency bandwidth of absorption peaks. The experimental results indicate that the data preprocessing provided is beneficial to follow-up operation, calculation and evaluation in such systems.