The mechanism of internal collissional fragmentation inside the Giant Molecular Clouds (GMC) is studied. It is known from observations that the GMC are a complex dynamical system of smaller condensations embedded in tenuous medium. Paired collisions of such “protoclouds” are considered as the basic mechanism determining the medium fragmentation and mass spectrum for the generated fragments. We used the SPH method for the simulation of 3D gas-dynamics processes. The process of collision of two identical “protoclouds” is considered in detail. We studied some variants of collisions for a wide range of initial impact parameter β. Our simulations showed that intensive gas fragmentation takes place in the system for all β. The yielded mass spectra depend on an assigned value of β and, in chosen range of impact parameter, are in good agreement with observational data for our Galaxy.