In a 3-wave mixing process occurring in some nonlinear optical medium when a † 1 mode interacts with both a † 2 mode and a † 3 mode, we theoretically study the squeezing effect generated by the operatorThe new 3-mode squeezed vacuum state in Fock space is derived, and the uncertainty relation for it is demonstrated, It turns out that S3may exhibit enhanced squeezing. By virtue of the technique of integration within an ordered product (IWOP) of operators, we also derive S3's normally ordered expansion. The Wigner function of new 3-mode squeezed vacuum state is calculated by using the Weyl ordering invariance under similar transformations.