[en] The heuristic model for description space-energy characteristics of the high-energy bremsstrahlung has been developed. On its basis the method for analytical estimation photonuclear yield of isotopes in wide range of atomic number (Z=20-80) and size of a target as well as of the electron energy (40...100 MeV) is proposed. The analysis of validity of the model assumptions has been executed by means of it comparison with the results of simulation using the program package PENELOPE/2006 [1] supplemented with database on the cross-sections of photonuclear reactions. It has been shown earlier that such simulation method provides close fit with the experimental results. As an example the reactions of practical interest ⁴⁸Ti(γ,p)⁴⁷Sc, ⁶⁸Zn(γ,p)⁶⁷Cu and ¹⁸⁷Re(γ,n)¹⁸⁶Re are presented.