Results of the researches of the crystalline structure of carbon steels martensite are analysed. Embedding of carbon atoms in steel (up to 1,7% mass. or $\cong$ 8 at.%) on one of the $a$, $b$, $c$ edges of the b.c.c. lattice of the martensitic phase (b.c.c. $\alpha$-Fe type) results in the increase of this edge and corresponding changes of the closely spaced edges. In this case, the crystalline structure of the martensite can be presented as a set of blocks of four distorted b.c.c. lattices with different sizes of the $a$, $b$, $c$ lattice edges. Under the ordered location of carbon atoms only on $c$ lattice edge, a pseudotetragonal structure arises, that results in an appearance of doublets of the diffraction lines. In the case of unordered (chaotic) location of the C atoms (on any of the lattice edge $a$, $b$, $c$) martensitic structure remains cubic one and the diffraction lines are broadening. The crystalline structure of martensite is well enough described also by root-mean-square displacements of the Fe atoms from positions of equilibrium caused by periodic insertion of the carbon atoms on $c$ crystal edges of b.c.c. lattice of the martensitic phase.