The method for investigations of magnetic field structures in subphotospheric layers of the Sun is elaborated. Observational results on the torsional oscillations of sunspots with the period 2.2—7.1 days were putted into bases of this method. Parameters of torsional oscillations and magnetic tubes in deep layers were determined. The magnetic flux tube forming a sunspot is a stretching formation. The radius of cross-section of magnetic tubes is the greatest near the solar surface and is approximately the same as radius of a sunspot umbra. In deeper layers it decreases enough rapidly. The longitudinal electric current appearing in a magnetic tube changes direction with the period of torsional oscillations. The density of a current and intensity of a longitudinal magnetic field in a magnetic tube increase with depth according to decreasing of the cross-section of the magnetic tube. An Alfven wave velocity averaged over length of a magnetic tube is in tens and hundred times less than the same velocity in a sunspot umbra. It decreases with an increase of the period of oscillations or of the magnetic tube length.