The problem of describing and methods for calculating the longitudinal form factor for taking into account the influence of longitudinal nonuniformity of heat release on the critical heat flux are briefly analyzed. An attempt is made to develop the method on the basis of some new physical assumptions. New relations are developed and suggested, the use of which made it possible to describe experimental data on critical heat fluxes in the case of heat release uniformly distributed over the length of tubes and fuel-rod assemblies.