Abstract: In the determinnation of force constants from frequencies and factorization of Gmatrix, an ordering relationship of Amatrix (may be n dimensional) relative to Lmatrix is found according to the ordering of symmetry coordinates. With the help of inverse unitary transformation, a general method to calculate F_R from constants F_R is established. The additivity of F_R depending on the symmetry block is determined to be true. All the force constants in non-planar and planar of urea, thiourca and sclenourca molecule were calculated by general valence force field. The calculated values of frequencies were compared with other data given in the literature. It was shown that the present calculation gives good agreement with the experimental results.