Take a certain expressway for example， this paper makes calculation and demonstration on key indicators of improving speed limit. Through calculation and comparison of the expressway horizontal and vertical linear index、transverse force coefficient、stopping sight distance、intercommunication and service area、roadside clear zone and other indicators after improving speed limit with the vehicle driving characteristics, the key control indicators for improving speed limit on expressways are put forward. It provides a good reference for expressway construction taking into account traffic safety and operation efficiency.