In order to simplify the calculation of threshold luminance difference, based on threshold luminance difference experiment calculation model of ANSI/IESNA RP800, two simplified calculation models were proposed with constant stimuli experiment and WeberFechner's Law， respectively.Negative contrast correction coefficient, identification time correction coefficient and age correction coefficient were obtained.A road lighting visibility was calculated with these two models and the model of RP800 as a case study.It is found that the visibility values calculated from these three models are in good agreement.