In order to predict the plastic shrinkage cracking of cement mortar and prevent it effectively， the cracking factors of the prediction equation（composition， constrained degree and segregated degree） were added and the range of the environmental parameter was expanded by flat plate method and eight-character model method based on the initial establishment of early warning mechanism for plastic shrinkage cracking of cement mortar.Thus the early warning mechanism for plastic shrinkage cracking of cement mortar was expanded. The results show that the seven-element constitutive equation of plain cement mortar without fibers and the nine-element constitutive equation of cement mortar with polyvinyl alcohol（PVA） fibers are established which can effectively predict the cracking of cement mortar. In addition， through combining the constitutive equations and their cracking criteria， the early warning mechanism for plastic shrinkage cracking of mortar is established， which can effectively reduce cracking by adding suitable PVA fibers after predicting the cracking condition of plain mortar correctly and ensure a good construction quality.