The focus thermal drift of micronano CT ray source is one of the important factors affecting image sharpness. The influence of focus drift of the ray source on image sharpness is analyzed through theoretical and simulation experiments. With the actual micronano CT system, experiment discovers that the focus drift is mainly slow thermal drift and the drift is positively correlated with the power of the Xray source, meanwhile the focus drift has certain randomness. On this basis, a focus drift correction method is proposed based on projection image feature matching. Firstly, a small amount of reference projection is rapidly acquired after the actual CT scanning, and the focus drift amount at specific angle is obtained according to result of adaptive feature matching between the actual projection and reference projection. Secondly, all the focus drift amounts in the CT scanning process are obtained with spline interpolation. Finally, the actual projection data are corrected according to the amount of focus drift, and through reconstruction the corrected image is obtained. Experiments show that the proposed method has high positioning accuracy, greatly reduces image distortion and improves image sharpness by nearly 10%.