  We present a systematic study on the strange particle production at the Large
Hadron Collider (LHC) in proton-proton (pp) collisions at $\sqrt{s}=$ 7 TeV
based on PACIAE simulations. Two different mechanisms accounting for single
string structure variations and multiple string interactions are implemented in
the simulations. These modifications give rise to increased effective string
tension in the Lund fragmentation model and generate more strange particles in
the hadronic final state. By comparing the results with a wealth of the LHC
data, it is turned out that the inclusion of variable effective string tension
is capable to reach an improved agreement between theory and experiment,
especially on the recently observed multiplicity dependence of strangeness
enhancement in pp collisions. This approach provides us a new method to
understand the microscopic picture of the novel high multiplicity pp events
collected at the LHC in the string fragmentation framework.
