All-solid-state polymer electrolyte (SPE) matrices prepared by molecular design are still needed to be further perfected with excellent performance. In this paper, a controlled-structure discotic liquid crystal (DLC)-based six-arm star copolymer was designed and synthesized from a DLC initiator (2,3,6,7,10,11-hexakis(2-bromoisobutyryloxy)triphenylene) via the sequential atom transfer radical polymerization (ATRP) of styrene and poly(ethylene glycol) methyl ether methacrylate (PEGMA). Here, this class of discotic liquid crystal star polymer is applied as an SPE in LIBs for the first time. By solution casting, a suitable self-standing SPE film composed of the six-arm copolymer and lithium bis(trifluoromethanesulfonimide (LiTFSI)) can be easily formed, and the film shows long-range molecular orientation after annealing. It is confirmed that the electrolyte shows wide electrochemical window (5.1 V) and high lithium-ion transference number (0.37). Especially, the ionic conductivity (1.46 × 10−4, S cm−1, 30 °C) of the obtained SPE is more than 8 times higher than that of the corresponding linear copolymer electrolytes. Furthermore, the results of battery performance demonstrate that the polymer electrolyte displays eminently reversible electrochemical reaction and outstanding cycling performance. The present work not only shows the advantages of DLC-based star SPE for LIBs but also paves the way for the design of SPE with excellent performances.