Humidity and density are important physical indicators to evaluate the quality of cigarettes. Proper humidity and density can improve the quality of the cigarettes and reduce the defective rate. To detect cigarette humidity and density, the terahertz time-domain spectra (TDS) of 3 cigarette sample groups (each group contains 11 samples) with identical density and different humidity and 2 cigarette sample groups (each group contains 14 samples) with identical humidity and different density, are collected using the time-domain spectroscopy system. The humidity calculation model which is based on the peak attenuation ln E and the mathematical expression between cigarette density and the spectral peak in terahertz time- domain are established. Compared with the traditional method of drying and weighing, the results obtained by the humidity calculation model show that the absolute error is less than 2.5% when the humidity is lower than 20%. The cigarette density and the spectral peak in terahertz time-domain are relevant. The correlation coefficient can reach 0.9639. The detection of cigarette humidity and density based on the terahertz time-domain spectroscopy is not only feasible but also with high accuracy.