In this study we present a theoretical investigation of the full-zone landscape of finite-momentum dark excitons in WSe2-MLs by solving the density-functional-theory (DFT)-based Bethe-Salpeter equation (BSE) under the guidance of symmetry analysis. The studies reveal the comprehensive valley-polarization landscape of finite-momentum exciton of WSe2 monolayer. Dictated by the crystal symmetry, the valley pseudospin texture over the extended exciton-momentum kex space exhibits rich structures, featured by the inherently full valley polarizations in the excitonic Kex, Kex′, and Qex,i valleys and also by the contrasted valley depolarizations for the exciton states lying in the ΓexMex,ī paths. Attractively, the superior valley polarizations of the intervalley dark excitons in WSe2-MLs are shown almost fully transferable to the optical polarization in the phonon-assisted photoluminescences because of the native suppression of exchange-induced depolarization in the second-order optical processes. The analysis of phonon-assisted photoluminescences accounts for the recently observed brightness, high degree of optical polarization, and long lifetime of the intervalley dark exciton states in tungsten-based TMD-MLs.