Disclosed is a parking assist system including a camera unit for photographing front or rear view of a vehicle, and a display unit for displaying a front or rear view image of the vehicle photographed by the camera unit, the system characterized by: a processor unit generating a first and second parking guide line, one being perpendicular to the other, at an area which is apart from the vehicle by a predetermined distance, and generating an estimated travel trajectory line based on steering angle information obtained from a steering angle sensor of the vehicle; and an overlay unit for overlaying the photographed front or rear view image of the vehicle on the first and second parking guide lines and the estimated travel trajectory line.