An analytical method for calculation of the critical energy of composite superconductors based on the theory of minimum propagating zones is presented. Both quasi-stationary minimum propagating zones and transient propagating zones are considered. The method, resolving itself into multiple integration, does not require the temperature field in the conductor to be determined. Such an approach facilitates dealing with cases allowing for temperature-dependent conductor properties and for the full boiling characteristic of the coolant. Formulae for the critical energy with regard to nucleate and film boiling are derived and sample calculations are performed. The results show that under good cooling conditions the enthalpy increase in the quasi-stationary minimum propagating zone approximately equals the minimum heat content in transient propagating zones.