In experimental validations of fusion blanket neutronics performance, tritium production rate is one of the most crucial measurement parameters. The number of ⁶Li atoms in the detector, as a normalization factor for calculating the tritium production rate, is a key factor determining the accuracy of measurement results and must be accurately calibrated. This paper specifically introduces the principles of calibrating the number of ⁶Li, the experimental setup and procedure, and the methods for quantifying uncertainties. For the first time, the number of ⁶Li atoms in a small lithium glass detector was calibrated using a germanium monocrystal monochromator to obtain 32.36 meV neutrons at the M5 horizontal channel of the China Mianyang Research Reactor (CMRR), with an uncertainty of 2.62%.