Abstract: Combined with the actual production of Nanjing Ziguang Fine Chemical Factory,the design principle for expanding the capacity of a 100 t/a pyromellitic dianhydride (PMDA) oxidation reactor to 210 t/a is introduced.Under the conditions that the oxidation reaction temperature is 435-445℃ and the temperature of molten salt,a high temperature carrier,is 380-390℃,the design size of the oxidation reactor is determined as 1 170 reaction tubes with Φ30×2.5 mm of root diameter.Through calculating the main equipment of the oxidation system,the potential capacity of existing equipment is fully utilized under the conditions that the unit consumption of raw material per ton of PMDA is 1.4 tons,the load of isotoluene catalyst is 60 g·h-1 and the operating space velocity is 4 000 h-1.The purpose of the expansion design is achieved.