The biphasic character of semi-crystalline polymer was modeled by the multi-mechanism (MM) constitutive relationships. Here, a comparative study between continuum damage mechanics (CDM) theory and Mechanics of Porous Media (MPM) approach, both related to the MM model, is performed. This comparison is based upon creep tests conducted on notched round bars made of PA6 semi-crystalline polymer to enhance a multiaxial stress state. For CDM model, the damage is classically described by a unique overall variable whereas the average of the local porosity at each phase level was considered for the MPM model. For each model, the optimization of the set of material’s parameters was carried out by combining the overall behavior of notched specimens subjected to creep loading, as well as the local information such as the distribution of porosity. It is found that both CDM and MPM models, each coupled with MM model correctly describe the overall creep behavior of the notched specimen if two damage variables are used. Moreover the MM/MPM model is more relevant for predicting porosity distribution.