The invention relates to a production method of ultra-fine heavy calcium carbonate slurry formed by size mixing, buffering, twice grinding and detecting, stabilization and factory testing. The methodcompletely solves the defects that the product GCC of D98 grade at home depends on import and domestic equipment cannot produce the product of D95-D98 grade. The production process is simple and reasonable and produces the product GCC of D98 grade which passes the paper coating test carried out by China National Pulp and Paper Research Institute, and the test of National Paper Products Quality supervision Inspection Center as well as accords with the requirements, thus providing new and better product GCC for industries of China, such as paper making, daily chemical industry institute, plastic, rubber, paint coating, PVC pipes, medicine, and so on. The method has good social and economic benefits and fills a domestic blank in the field.