Disclosed is a die pinching device which is an air tightness mechanism to form a vacuum environment for the pinched die. The invention comprises a base, a long shaped frame which is connected fixedly and vertically on the base with one end of a long shaft of the frame; a top which is bridged at the other end of the long shaft of the frame and is arranged above the base, so as to correspond up and down to the base and form a die pinching space for the pinched die to be arranged between the top and the base; an air tight pipe shaped cover which can do reciprocating linear movement along the long shaft of the frame and between an air tight position and starting position; when in the air tight position, the cover is positioned in the die pinching space and is around the pinched die; a first closed end part which is arranged on the base and is provided with a ring shaped first closed connecting end which is used to be connected in butt in corresponding and coaxial air tightness with one end of a pipe axis of the cover on the air tight position; a second closed end part which is arranged on the top and is provided with a ring shaped second closed connecting end which is used to be connected in butt in corresponding and coaxial air tightness with the other end of the pipe axis of the cover on the air tight position. The invention can achieve the effect of reducing the integral height of the die pinching device, which is convenient for operation and maintenance.