Abstract: In this paper,calculations of force constants of molecular vibrations are carried out by using Wilson GFmatrix method.In the determination of force constants from frequencies and factorization of Gmatrix,an ordering relationship of Amatrix(may be n dimensional) relative to Lmatrix was found according to the ordering of symmetry coordinates.With the help of inverse unitary transformation,a general method to calculate Ft from constants Fs was established.The additivity of Fr depending on the symmetry block was determined to be true.All the force constants in non-planar and planar of urea,thiourea and sclenouroa molecules were calculated by using the general va-leine force field.The calculated values of frequencies were com-pairec with other data given in the literature,and it was shown that the present calculation is in good agreement with the experimental