A coupling device of jigs includes a foundation, a tube, a plurality of balls, and a piston base. The foundation has a chamber, in which a part of the tube is inserted. The tube has a plurality of through holes for housing the balls. The piston base is received in the chamber, and fitted to the tube. An inner surface of the piston base has a circular groove and an abutment surface. The piston base can be moved along an axial direction of the tube between a first position and a second position. When at the first position, a part of each ball is inside the circular groove; when at the second position, an area where the abutment surface abuts against each ball is not merely a single point. Whereby, the force applied on the abutment surface is dispersed, and therefore the processing accuracy of workpieces is ensured.