Obvious differences exist in the complexity of Pm waves obtained by deep seismic sounding (DSS) in different tectonic units. These differences are closely related to deep structural features. In this paper, a method is proposed for computing the complexity of seismic waves on the basis of its transient features and duration. For an ancient stable block, the Moho complexity coefficient is small, which reflects the feature of first order discontinuous interface. In contrast, for a strongly active block, the Moho complexity coefficient is large, which reflects the feature of crust-mantle transitional zone. Data processing was carried out with respect to a DSS profile which passes through the northeastern edge of Qinghai-Xizang Plateau. The result was interpreted dynamically.