Abstract: For the CT system,the problem of the shape of the medium is determined by the received information of the detector.firstly,based on the analytic geometry principle,We analyze the relationship among the rotation center,the X-ray direction,the medium absorption rate,and the data received by the detector.Then,according to the data measured by the calibration template,the parameters of the CT system are obtained by using regression analysis,double search and other algorithms.Finally,based on the Fourier Slice Theorem,an imaging model of CT system is established.Through the filtered back projection method in image reconstruction and the corresponding translation transform,the gray matrix of the unknown medium is obtained so that the shape of the medium is determined.Experimental results show that this method has strong reliability and great accuracy in image reconstruction of CT system.