One of the main causes of degraded performance is the defects in the bulk Cu2ZnSnS4 absorber layer of the kesterite solar cells. In this study, a numerical simulator SCAPS-1D used to understand the effects of each point of antisite defects with the presence of the band tail on the electrical characteristics of Cu2ZnSnS4 solar cells stepby-step. The effects of capture cross-section of Sn-Zn deep multilevel defect and defect concentration of Cu-Zn + Zn-Cu on cell performances have been analyzed. The results highlight that the control of capture cross-section of the multilevel defects is an important key to take into account for further improvements of Cu2ZnSnS4 solar cell performance.