The results of the previous investigations of martensite crystal structure in the carbon steels, in which, based on the doublet splitting of some XRD lines, the conclusion on tetragonality of martensite was made, is analysed. As proposed, the crystal structure of martensite in the carbon steels is considered as a system of the lattice blocks with C atoms at the block axes and the distorted lattices without carbon atoms around the blocks. Carbon concentration in the steel specifies quantity of the blocks. Edges of the lattices in the blocks and outside them have different sizes depending on the distance to the block axis with carbon atom. As defined, the martensite crystal structure in the carbon steels is pseudotetragonal or trigonal. New approach is proposed for an explanation of a great width value of the martensite XRD lines in the carbon steels.