All-solid-state lithium metal battery (ASSLB) is one of the most promising candidates for next-generation batteries due to its intrinsic advantages of high safety and high energy density. However, the two critical challenges of high interface resistance and Li dendrite growth still hinder the development of ASSLB towards practical application. The critical current density (CCD), which is the maximum current density a lithium metal battery can operate without interface resistance and Li dendrite caused failures, usually measured in a symmetrical cell (Li|electrolyte|Li), has been widely tested and reported in the ASSLB studies. This crucial indicator has been used to evaluate the qualities of the solid electrolyte (SE), SE|Li interface, and Li anode. However, the absolute value of CCD is not solid enough to represent the above qualities, which is followed by significant deviations with the long-term cycling current densities of the symmetrical cells and full cells. Herein, using garnet and sulfide as template electrolytes, we systematically conclude the factors influencing the credibility of CCD through measurement and statistics. The thickness-dependent, cycling time(capacity)-dependent, comparability across different kinds of electrolytes, and different failure mechanisms in CCD tests are discussed. The depletion factor (DF) was proposed to correct the capacity-dependent properties as the missed information in CCD measurement. The relationship between the current density achieved in the CCD test and the current density used in symmetrical cells and full cells cycling was analyzed. Herein, we seek to point out the gap between the absolute values of CCD and the real properties of ASSLBs, help the community to productively screen the designs and chemistries in ASSLBs, and push ASSLBs into practical applications.