Abstract: P-sets(packet sets) is a set pair composed of internal P-set Xand outer P-set XF, while the (σ,τ)-generation of assistant sets of P-sets is also a set pair composed of σ-generation of internal assistant set Aσ(X) and τ-generation of outer assistant set Aτ(XF). Based on the above knowledge, (σ,τ)-expansion model of P-sets is proposed. The relationship theorem between P-sets and its (σ,τ)-expansion is presented. A series of propoties about the (σ,τ)expansion of  P-sets are discussed. (σ,τ)-expansion model of P-sets expands the research field of P-sets.

Key words: P-sets, assistant sets of P-sets, (σ,τ)-generation of assistant sets