The invention, which belongs to the field of error compensation of a numerically-controlled machine tool, provides a modeling and compensation method of a radial thermal drift error of a spindle of ahorizontal numerically-controlled machine tool. Two thermal drift errors along the radial direction of a spindle of a umerically-controlled machine tool and corresponding key point temperatures are tested; on the basis of a thermal tilt deformation mechanism of the spindle, a thermal inclination angle of the spindle is obtained and the correlation between the thermal inclination angle and the temperature difference between the left side and the right side of a spindle box is analyzed; according to the positive or negative situation of the thermal drift errors of the tested two points and stretching or contraction situations of the left side and right side of the spindle box, a thermal deformation situation of the spindle is classified and thermal drift error models under various thermal deformation attitudes are established; the influence on the model prediction result by the structural dimension of the machine tool is analyzed; and during real-time compensation, the thermal deformation attitude of the spindle is automatically determined based on the temperatures of the key points and the spindle is compensated by selecting a corresponding thermal drift error model automatically. Therefore, the determination of the thermal deformation attitude of the spindle of the numerically-controlled machine tool is realized during the processing process; and on the basis of the thermal deformation mechanism, the radial thermal drift error of the spindle is predicted.