In the flat panel detector, the ring artifacts caused by the defective and response non-uniformity pixels will affect the quality of X-ray computed tomography (CT). In order to solve the issue, the linear correlation between pixel response and tube current is applied, and a ring artifact removal method based on detector calibration is proposed. The pixels are detected, whose response is constant under different tube currents. Then the pixels with the response varying randomly or quickly reaching up to the maximum value are detected, and the correlation coefficients between each pixel channel response and the tube current are calculated. The pixels detected with the above mentioned methods are written into defective pixels map and corrected. With the reference of average response of all pixels under each tube current, the relationship between response and reference curve of the pixels under the same tube currents is calculated to obtain the identical correction matrixes of the detector. The output responses of the pixel are corrected according to the defective pixels map and the identical correction matrixes. Experimental results show that the proposed method can removes the ring artifacts effectively, and improves the signal to noise ratio of reconstruction image. In addition, it solves the problem of threshold selection with the existing defective pixal detection methods, which can be applied to different types of detectors.