Abstract: By using the constraint and dimension driven concept in CAD software, some type of simulation for planar mechanisms is created. The given driving dimension of input link is modified, and the driven dimensions of output link are changed automatically. The displacements of output link relative to the motion of input link are recorded and fitted into continuous trajectory by using Excel software. Then the velocity and acceleration are derived from the equation of trajectory. The results of computer simulation and fitted equation show that simulation of constraint and dimension driven mechanism is not only straightforward and highly efficient, but also has the advantages of ensuring accuracy and repeatability.