In order to study the occurrence regularity of early-age plastic shrinkage cracking, a series of indoor and outdoor experiments have been done in this paper. The synthesized discriminant index which is used to discriminate the situation that whether the early-age plastic shrinkage cracking happens or not has been put forward in this paper. It includes the index of unit volume accumulated evaporation besides the index of evaporation rate. Meanwhile, using Bayes Discriminant Method, based on the former indexes, the critical figure which is in connection with given environment conditions has been obtained and it can be used to detect whether early-age plastic shrinkage cracking happens or not by plotting the sense data which comes from the check specimen. The precision of prediction results that whether early-age plastic shrinkage cracking happens or not has been raised substantially by using this kind of discrimination method. The theory and method are useful for engineering application.