The standard JJF 1809-2020 specifies the calibrate specification for Retroreflectometers. Retroreflectometers are used for the measurement of rays of light reflected on the surface of an object under conditions close to vertical incident rays. This specification applies to calibrating Retroreflectometers to ensure the accuracy and Reliability of their measurement results. Citing related documents such as JJF 1059.1, JJF 1796, JT/T 688-2007 and JT/T 690, the standard specifies terms and definitions to be followed in the calibrate process, such as inverse reflection, luminous intensity coefficient Rr, inverse reflection coefficient RA and inverse reflection coefficient RL, etc. Through the implementation of this specification, the Accuracy and Stability of Retroreflectometer in various application environments can be effectively guaranteed.