Abstract: To resolve complicated coupling geometry problem,a method based on freedom analysis is proposed.Some constraints are added to reduce the number of variables to be iterated.The initial values of these constraints are gotten from the original sketch.The constraints not being used during clustering will be taken as objectives to be satisfied,and the derivative matrix is gotten with numerical method.By iterating the values of these variables,the constraints can be satisfied.With this method,the calculation process will be more stable and faster than conventional methods.This method combines the merits of numerical methods and algebraic methods.Several examples are given to demonstrate the view.