A new concept called isoconversional state diagram, which can be used to predict the kinetics of single-step condensed phase reactions, is introduced. A state represents a certain extent of conversion degree α in a reaction. The construction of the isoconversional state diagram is based on the isoconversional state equation, which is a piecewise linear equation about 1/T and lnβ, where T is the temperature and β is the heating rate. The slope of the linear equation is controlled by the activation energy Eα and its intercept contains the inherent information of the kinetic triplet, i.e., the pre-exponential factor Aα, the activation energy Eα and the reaction model f(α). Consequently, the geometric methods for nonisothermal and isothermal kinetic predictions are derived. The latter reflects the physical meaning of the relationship between reactions under isothermal and nonisothermal conditions, i.e., the time to advance from αi to αi+1 at isothermal temperature Tiso is equal to the time to heat from Tiso to under heating rate , where Tiso, and must be determined from the isoconversional state diagram.