Provided is a method for preparing sulfuric acid by using hydrogen sulfide. The method comprises the following steps: (1) performing a reduction-oxidation reaction between an H2S feed gas and oxygen to prepare SO2; (2) cooling the product acquired in step (1) to a temperature between 390° C. and 430° C., then performing a catalyzed oxidation reaction with oxygen; and (3) cooling the product acquired in step (2), then further cooling to a temperature between 60° C. and 120° C., collecting H2SO4 product. Also provided is a heat exchanger, comprising a housing and several glass pipes arranged within the housing along the direction of a long axis of the housing, arching between two lateral walls thereof; the adjacent glass pipes are connected head-to-tail. The method provides great hydrogen sulfide removal efficiency, simple process flow, and allows for economic efficiency of apparatus and reasonable utilization of energy.