The utility model discloses a device for increasing the yield of 105% fuming sulfuric acid. The device comprises a fuming sulfuric acid tower, wherein the fuming sulfuric acid tower is provided with two stages of upper and lower absorption towers, the lower part of a lower first-stage absorption tower is connected with a concentrated fuming sulfuric acid circulating tank, a concentrated acid pump is installed in the concentrated fuming sulfuric acid circulating tank and connected with the upper part of the first-stage absorption tower in a return manner through a cooler I, the lower part of an upper second-stage absorption tower is connected with a dilute fuming sulfuric acid circulating tank, a dilute acid pump is arranged in the dilute fuming sulfuric acid circulating tank and connected with the upper part of the second-stage absorption tower in a return manner through a cooler II, and the dilute fuming sulfuric acid circulating tank is provided with an external 98% sulfuric acid inlet. The device has the benefits as follows: on the premise that 80,000 tons of chlorosulfuric acid products every year are guaranteed, the yield of the 105% fuming sulfuric acid is increased to 80,000 tons from originally 40,000 tons every year; the 105% fuming sulfuric acid is increased, and the device can produce 107% fuming sulfuric acid products and 115% fuming sulfuric acid products needed by the market according to market needs.