As a result of the use of a threecomponent geophone to receive seismic signals in TETSP2 tunnel seismic advance detection system; it is urgent to separate the mixed information such as primary wave and secondary wave in seismic wavefield. In this paper, the timedistance curve of the reflected longitudinal and transverse wave in the tunnel is deduced; the applicability of the τp transform in the tunnel seismic advance detection is theoretically analyzed based on Taylor′s formula; and the relationships between nodal increment and slowness of τp transform and reflection interface dip angle are given. And then the whole wavefield in the twodimensional tunnel space under simple conditions is simulated; the reflection characteristics of different wavefields are analyzed; and the characteristics and differences of reflection Pwave and Swave in τp transform domain are compared under different dip angles. The results show that: (1) The apparent velocity of reflection transverse wave under different dip angles varies, and the apparent velocity increases with dip angle decrease. (2) The τp transform can separate wavefield relying on different apparent velocity between primary wave and secondary wave; the method can well separate the wavefield when the dip angle of low speed zone in front of tunnel face is no less than 40°; but when the dip angle is small, the firstorder Taylor expansion of timedistance curve has a large error, which makes the effect of wavefield separation bad.