The Flory-Schrdz distribution or the most probable distribution was deduced in literature．for the molecular weight distribution functions of linear polymers synthesized by condensation and addition reactions in some simple eases．An alternative theoretical way for deducing these equations is given according to the most probable state by using the basic principle in statistical physics for two model systems of typical linear polymers

the forming of which obevs the mechanism of free radical termination by combination and disproportionation Then the Hory-Schulz distribution is obtained quite naturally This theoretical method is simple and easy without any additional supposition．It is hoped that this study could be helpful in understanding the physical foundation of the Flory-Schulz distribution.