A crustal flow model has been previously used to explain the crustal extension of the Tibetan Plateau. However, the existence of massive crustal flow in the central plateau is still controversial. We conducted a joint inversion of receiver functions and surface wave dispersions from the 2-D broadband seismic array SANDWICH deployed in the central plateau. The crustal S-wave velocity structure with high vertical resolution shows a low-velocity layer (LVL) in the middle-lower crust beneath most stations. The S-wave velocity of this LVL is mostly within 3.0-3.4 km/s, reflecting a melt volume percentage (MVP) ≤ 7%, except at two stations. Our study suggests that there is not a high enough melt volume in central Tibet to develop crustal flow, which requires an MVP ≥ 7% to decrease rock strength. The formation of extensional structures in the central plateau may contribute to ductile deformation in the middle-lower crust but not crustal flow.