Crustal anisotropy beneath a dense broadband seismic array across the Longmenshan fault belt is measured based on P-to-S converted phases from the Moho and an intra-crustal interface. The crustal thickness and the average Vp/Vs values are also estimated by a new H-κ-c method. The crustal anisotropy in Aba sub-block mainly comes from the middle-lower crust and the NW-SE fast polarization directions (FPDs) may reflect the direction of the crustal flow. A sharp variation of FPDs is observed in the vicinity of the Longriba faults, combined with the Vp/Vs values and other geological and geophysical observations, we suggest the Longriba faults may block the eastward flow of crustal materials. East of the Longriba faults, the consistence between the FPDs and the direction of the maximum horizontal compression, and low Vp/Vs values indicated that the crustal thickening may be the dominant deformation mechanism in the Longmenshan sub-block. The crustal anisotropy in the Longmenshan fault belt is mainly manifested as fault-parallel FPDs, probably related to fluid-filled fractures in this area. The Sichuan basin is weakly anisotropic and the NE-SW FPDs may reflect the tectonic strike. Combined with previous observations, our results suggest that the crustal flow and crustal thickening are co-exist in the crustal deformation in eastern Tibet.