The traditional process of train headway was introduced, the weakness of which was explained that could not guaranteerailway capacity and timetable stability in railway system. The method of UIC406 capacity was researched based on blocking time model,and the model of headway in the fixed block signal system and the moving block signal system was built based on the characteristic ofdomestic railway system, as well as the theoretical calculation method was pushed down. The reasonability of headway time model wasvalidated with the railsys software.