Pantograph is an important equipment of current collector for the electric train. The abrasion of the pantographic slide affects the coordination of pantograph-catenary system. Automatic measurement of pantographic slide abrasion is one of the important means to realize the automatic fault inspection of pantograph. According to the image characteristics of pantographic slide captured by the vision measuring system, an accurate recognition algorithm for upper and lower edges of the slide is proposed. The proposed algorithm is fulfilled by employing the accurate sub-pixel edge location method based on partial area effect. By comparing with other common edge extraction algorithms, the feasibility and superiority of the proposed algorithm are proved.