All-solid-state Li-O2 batteries are receiving intense interest because of the substitution of solid electrolytes for toxic and flammable liquid electrolytes. However, new issues are arising in the aspect of the electrolyte cathode interface. On the one hand, in a traditional sandwiched battery structure, the reaction sites of the cathode are restricted to the finite planar electrode-electrolyte interface, resulting in limited performance of all-solid-state Li-O2 batteries. On the other hand, integrating the electrolyte with the cathode to achieve good interfacial contact often requires complex sintering processes. Herein, this work reports a solid electrolyte cathode assembly (SECA) which consists of a dense Li1.5Al0.5Ge1.5P3O12 (LAGP) layer and a carbon coated porous LAGP layer fabricated by facilely one-step sintering. As a result, Li-O2 batteries adopting the SECA showed a relatively high discharge capacity of 0.48 mAh cm-2 at 5 μA cm-2. Besides, the batteries could sustain six full cycles with a restricted capacity of 0.08 mAh cm-2 at 10 μA cm-2. It was found that the high capacity can be attributed to the high surface area of porous cathode structure.