The invention relates to a positioning and clamping device for milling small-size flat long and thin parts. The positioning and clamping device is characterized in that: a groove is formed on the lateral surface of a clamp body (1); at least two positioning holes are formed on the side of the groove; a limit pin (3) is arranged on each positioning holes; a guiding element (8) is connected below the clamp body (1), and a guiding groove is formed on the middle part of the guiding element; a clamping element (4) is connected to a holder (9); the holder (9) is connected with a cylinder (7) and is positioned in front of the groove of the clamp body (1); the clamping element (4) is provided with clamping arms in a direction which is opposite to the clamp body (1); the clamping arms of left and right sides are positioned in the guiding groove of the guiding element (8); the cylinder (7) is positioned below the guiding element (8) and is connected with the holder (9) through an expansion link in front of the guiding element; and the positioning and clamping device is arranged on an operating platform of a numerically controlled milling machine. The positioning and clamping device can improve the integral machining accuracy, machining quality and the production efficiency of machining the parts.