We constructed a Li3V2(PO4)3/Li1.5Al0.5Ge1.5(PO4)3/Li3V2(PO4)3 symmetric all solid-state Li-ion battery. Since the rechargeable capacity of Li3+x V2(PO4)3 anode is lower than that of Li3−x V2(PO4)3 cathode, the symmetric cell capacity is restricted by the anode capacity. So, the improvement of Li3+x V2(PO4)3 anode properties was tried using mechanical milling to uniformly mix Li3V2(PO4)3 and carbon. The charge and discharge capacity of Li3V2(PO4)3/C using mechanical milling was greatly increased compared to Li3V2(PO4)3/C using hand milling. The structure change with the insertion and extraction of lithium confirmed using ex-situ XRD measurements. The Li extraction/insertion of Li3V2(PO4)3 with a NASICON structure can proceed to the reversible expansion/contraction of the lattice due to the structural strength and flexibility of NASICON framework with the corner-sharing matrix. The discharge capacity of the all solid-state battery per Li3V2(PO4)3 in cathode weight achieved 92 mAh g−1 by good dispersion state of Li3V2(PO4)3 and carbon using mechanical milling.