The invention discloses a probe servo mechanism for eddy current inspection of a main bolt inspection machine of a nuclear pressure vessel, which is characterized in that the transmission mechanism comprises a linear guide rail, a constant-force leaf spring, a turnover seat, a pressure bar, a probe holder and a spring, wherein one end of the turnover seat is provided with a vertical bend and the other end thereof is provided with a support; a rectangular block is welded near the opposite side of the support; the pressure bar is of an L-shaped structure, a U-shaped fixture is respectively arranged at both ends of the pressure bar, the U-shaped fixtures are respectively connected with the support on the turnover seat and the arc-shaped probe holder and pined through cylindrical pin shafts, and the probe holder is attached to a main bolt; and the spring is fixed in the middle of the pressure bar through a dowel, and the other end of the spring is connected on the rectangular block of theturnover seat which is clamped on the linear guide rail and connected with the constant-force leaf spring fixed on the linear guide rail. The probe servo mechanism realizes the automatic inspection for the main bolt of the pressure vessel at the nuclear power station, and the automatic inspection structure is stable and does not swing and the detection signal is stable.