The invention provides an inertial measurement unit and a single-axis servo successive inclinometry method. An inertial component adopts two fiber-optic gyroscopes and two accelerometers, the size of the inertial measurement unit is reduced, through the control by a servo motor based on the first fiber-optic gyroscope and the minimum hole inclination servo successive inclinometry method and the control by the servo motor based on the first accelerometer and the maximum hole inclination servo successive inclinometry method, the issues of successive inclinometry of a minimum hole inclination and a maximum hole inclination are solved, the azimuth angle, the maximum hole inclination and the tool face azimuth of a borehole are successively omnibearingly measured, and then the track of the borehole is successively obtained. Meanwhile, the minimum hole inclination servo successive inclinometry method is controlled by the servo motor based on the first accelerometer, so that drifting of gyroscopes caused by successive change of the working face in the process of practical work can be decreased, the measuring error is reduced, the one-time work duration is prolonged, and work efficiency is improved.