The present invention relates to a method and device of obtaining a beam hardening correction coefficient for carrying out beam hardening correction on computed tomography data. The method includes the steps of: firstly, acquiring an original reconstructed image and an original sinogram of an object of a particular size; secondly, obtaining an error-reduced sinogram after processing the original reconstructed image by error reduction; thirdly, sampling and calculating an average value of the original sinogram and an average value of the error-reduced sinogram; fourthly, optimizing the original sinogram according to the error-reduced sinogram to determine a coefficient vector of optimization function for the object of the particular size; and finally fitting the coefficient vector of the optimization function of the original sinogram to obtain the beam hardening correction coefficient for the object of the particular size.