The present invention relates to the preparation methods of diagnostic X-ray composition. The composition contains the pharmaceutically acceptable intracorporal non-ionic x-ray contrast agent of load. More particularly it relates to the method that the second level of X-ray composition produces, the composition contains the x-ray contrast agent of high solution temperature. When the method for the present invention is used, it avoids precipitating and reduces the degradation of contrast agent. The method of the present invention includes be heat-treated at a low ph to the x-ray contrast agent of iodate.
