The invention discloses a boring spindle device which comprises a sliding table transmission mechanism and an electric brush slip ring mechanism, wherein the sliding table transmission mechanism is fixedly connected to the front part of a hollow boring spindle (25); the electric brush slip ring mechanism is fixedly connected to the rear part of the hollow boring spindle (25); the hollow boring spindle (25) rotates, when the radial dimension of a required rotary cutter changes, a pinion (11) and a big gear (13) correspondingly meshed with the pinion are driven by the rotating of a stepping motor (39); and a screw rod (21) is driven to rotate by the big gear (13) so as to push a first nut (20) to move radially and push a sliding table (18) and a cutter table (17) fixedly connected to the first nut (20) to move radially together, so that the radial feeding is realized in the machining process. A shell of the stepping motor (39) and the hollow boring spindle (25) rotate together, and leads (a1, a2 and a3) of the stepping motor (39) are in contact with the electric brush slip ring mechanism arranged at the tail part of the hollow boring spindle (25).