Current differential protection puts forward high requirements on real-time data transmission, large transmission delay is likely to cause the refusing action of relay protection equipment or misoperation. Differences in organizational structure and communication equipment lead to obvious uncertainty of channel delay. This paper analyzes the influence factors of delay protection channel. On the basis of the time delay probability density distribution function of communication equipment, a longitudinal differential protection channel random time delay model based on the probability distribution is studied. The model can reflect the channel delay uncertainty. Further the probability determination method of relay protection equipments misoperation and refusing action is given. The results can be used as a reference for electric power system relay protection channel optimization configuration.