Abstract: In this paper, the following problems are discussed:1) the reason of the coeftcient of internal energy (e. g. strain energy or strain complementary energy) being 1/2, and of external energy (e. g. potential or complementary energy of external loads) being 1;2) a correct view of the replacement of effective nodal loads; 3) a simple method of establishing ‘Sharp Function’; 4) the displacement model and the stress model.