NASICON-type Li1+xAlxTi2-x(PO4)3 (LATP) is a representative solid electrolyte with high ionic conductivity, wide electrochemical window, superior air/water stability, as well as low toxicity and manufacturing cost. The rapid development of LATP, however, is hindered because of the side reaction between LATP and Li metal. To address this issue, here we focused on the electrochemical failure of the LATP-based lithium metal batteries with varied characterization. Herein, we found that the degradation of LATP led to the formation of cracks, which would decrease the Li+ diffusion coefficient and cause severe concentration polarization. The bad interfacial Li+ transport kinetics was found to be responsible for the rapid discharge capacity fading and cell failure of the solid-state batteries. The AM-FM and finite element analysis indicated that the decomposed LATP region possesses relatively low Young鈥檚 modulus and large volume, along with a nonuniform degradation reaction. The large elastic and volume mismatches were blamed for the stress concentration, which means that LATP undergoes stress cracks. We highlight that the inhomogeneity of the decomposed reaction played an important role in the cell failure of LATP-based lithium metal batteries, which could be advantageously used to reach interesting battery performance.