Abstract: Parking Guidance Information System (PGIS) is a technology which applies computer, information and multimedia etc. into traffic management. It is one of the important components of Intelligent Transportation System; This paper first analyzes the characteristic of dynamic route guidance in PGIS according to the requirement of real-time guidance, then introduces the characteristic of a natural algorithm—ant algorithm and the basic procedure when it is used in searching for the optimum route; a simulation experiment shows that the method has high searching efficiency and can be used in dynamic route guidance.