  Based on an isospin dependent quantum molecular dynamics model we studied the
influence of a medium correction of an isospin dependent nucleon nucleon cross
section on the fragmentation at the intermediate energy heavy ion collisions.
We found that the medium correction from an isospin dependent nucleon nucleon
cross section increases the dependence of the fragmentation on the isospin
effect of in-medium nucleon nucleon cross section, at the same time, the
momentum dependent interaction (MDI) produces also an important role for
enhancing the influence of the medium correction on the isospin effect of
two-body collisions in the fragmentation process. In this case, the dependence
of the multiplicity of intermediate mass fragments $N_{imf}$ on the isospin
effect of two-body collision due to the medium correction and MDI, is a probe
for extracting the information on the isospin dependent nucleon cnucleon cross
section in the medium correction.
