To solve the intractable slagging problem in biomass utility boilers, the effects of Si, Al, K, Cl, S, and initial slagging layer on slagging were performed by comparing the distinct slagging characteristics of two cotton stalks burned in utility grate furnaces. The criterion numbers of slagging, namely, Cl ratio (Cl+K2O+Na2O)/(SiO2+Al2O3) and S ratio (Svolatile+K2O+Na2O)/(SiO2+Al2O3), were proposed quantitatively. When Cl ratio and S ratio are higher than 2.4 and 1.9, respectively, the biomass is easy to slag; by contrast, the slagging is low when Cl ratio and S ratio are lower than 1.0 and 0.5, respectively. The slagging growth mechanisms were further improved by coupling the alternating layer structure of the whole slagging, which was formed by the re-enrichment of fine particles that primarily contained high concentrations of K, Na, Cl, and S in the form of KCl and K3Na(SO4)2 and by the re-capture of coarse large particles that primarily contained higher Si, Al and so on. K3Na(SO4)2, originated from the interaction between sulfates, promotes the growth of the slagging. Nonetheless, the influence of K3Na(SO4)2 on slagging is minimal in comparison with that of KCl. The disruption or inhibition of the initial slagging layer significantly weakens slagging.