Li7La3Zr2O12 (LLZO) stands out as a promising material for solid-state batteries due to its superior performance. However, the lithium dendrite growth in LLZO significantly affects battery performance due to high electronic conduction of LLZO. Herein, amorphous Li3BO3 (ALBO) is introduced into LLZO to construct a three-dimensional continuous grain boundary with lithium ion conductivity and electron-blocking property to suppress lithium dendrites. The symmetric cells of ALBO-LLZO achieved a high critical current density (CCD) of 1.1 mA·cm−2 and cycled stably for 2000 h at 0.3 mA·cm−2. The capacity retention of LFP/1 ALBO-LLZO/Li battery retains 84.6 % after 200 cycles at 0.2 C, room temperature. This research offers a potential solution to enhance the performance of the garnet electrolyte for ASSBs.