Parking-lines recognition is the precondition in vehicle automatic parking system. A Parking-line Detection Method Based on Edge Direction is proposed. Transform the gray images into edge images using median filter, edge detection. Pick out linear edges in the edge images using Hough transfer. Define the signs of linear edges and propose their determinant algorithm. Based on the algorithm, determinate the sign of each linear edge and recognize the parking-line according to the sign of each linear edge. The experimental results show that this algorithm is of the reliability and can satisfy real-time request.