In this paper, magnetic field and hydrostatic pressure effects on magnetism of ZnCr2S4 were investigated. Upon cooling the sample at 0.5 T to 2 K then warming back, the magnetization displays irreversibility between the cooling and warming sequence at temperatures around incommensurate–commensurate antiferromagnetic transition TN2. With increasing magnetic field or hydrostatic pressure, the irreversibility is gradually suppressed, although the thermal hysteresis is shifted to higher temperatures under pressure. The observed thermal hysteresis is attributed to a structural transition and evolution of different magnetic phases upon cooling and warming.