Disclosed are a positioning device and a method for an automatic medicine dispensing system. The method comprises the steps of: acquiring a needle positioning image vertically taken from bottom to top; performing grey-scale treatment on the needle positioning image to acquire a binary image; acquiring coordinates of an end point (N) of a needle (62) according to the binary image; generating a displacement compensation instruction according to the coordinates of the end point (N) and a pre-set distance between a camera (S1) and a needle bayonet (69); a clamping component (2) and a liquid injection component (6), according to the displacement compensation instruction, moving relative to each other to realize displacement compensation. The device and the method allow the needle (62) to accurately align to a pre-set insertion position of a medicine container (101), so as to accurately and quickly insert the needle into the medicine container (101) from the pre-set position, thus improving the medicine dispensing success rate and medicine dispensing efficiency.