Spectral range and signal-to-noise ratio (SNR) are important parameters to evaluate the performance of terahertz time-domain spectrometer (TDS). To solve the calibration problems of spectral range and SNR for TDS, the composition and principle of TDS were introduced. The advantages and disadvantages of the commonly-used calibration methods were compared, and one of the methods was selected to design the parameter calibration method of terahertz time-domain frequency-domain SNR. The frequency range corresponding to 1/M of the maximum amplitude of signal in the frequency domain was taken as the spectral range, and the influence of M value on spectral range was studied. The larger the M value, the wider the spectral range. When M value was greater than or equal to 50, the spectral range changed little. The signal and noise of the time-domain signal were defined, and the time-domain SNR was calculated. Using the frequency-domain power spectrum of air as the signal, the frequency-domain power spectrum in the light path covered by matal plate was taken as the noise, and the frequency-domain SNR was calculated. The calibration experiments of spectral range and SNR were carried out, and the influence of humidity variation on spectral range and SNR parameters of TDS was studied by contrast method. When the relative humidity was less than or equal to 50%, the influence on spectral range and time-domain SNR was not obvious. When the relative humidity was greater than 50%, because the absorption of water vapor increased sharply, the spectral range and SNR decreased sharply.