The noise in tunnel affects the driving environment and safety much； as a result, it is very important to study the propagation rules and detection schemes of it. The dB, distribution rules, reverberation time and frequency spectrum characteristics of the noise in tunnel are studied by theoretical calculation and site monitoring； and then the noise detection schemes are discussed. Some conclusions are drawn as follows: 1) The longitudinal distribution rule of dB of noise in tunnel is largest in the middle and smallest at the ends; and the dB of noise in tunnel increases a lot far away tunnel entrance of 50 m. 2) The direct sound is the main source of noise in tunnel within tunnel horizontal crosssection; the first reflected sound has a great influence on noise in tunnel at the focusing point of sound; the acoustic environment in tunnel is worsened by reverberant sound. 3) The main noises in tunnel are medium and low frequency noises and show clear bimodal shapes; the peak values of low frequency noise and medium frequency noise are 100 Hz and 1 200 Hz respectively. 4) The reverberation time in tunnel is related to shape of tunnel crosssection, average sound absorption coefficient of tunnel boundary and noise frequency. The reverberation time decreases with the perimeterarea ratio of tunnel crosssection, sound absorption coefficient of tunnel boundary and noise frequency increase. 5) The Aweighted sound pressure, frequency spectrum characteristics of noise and reverberation time should be included by the detection parameters of noise in tunnel; the tunnel length, shape of tunnel crosssection and technical level should be considered when make arrangement of noise monitoring points.