The present disclosure relates to a method and an apparatus for self-heat-extracting flash evaporation of a sulfuric acid alkylation reaction product. There is provided a method for self-heat-extracting flash evaporation of a sulfuric acid alkylation reaction product. One step is to coalesce and vaporize a preliminarily distributed sulfuric acid alkylation reaction product to cause preliminary vaporization of a hydrocarbon therein, thereby taking heat away and preliminarily separating the hydrocarbon from sulfuric acid. Another step is to subject the preliminarily separated alkylation reaction to reinforced separation, where the hydrocarbon is further vaporized to take heat away and further separate the hydrocarbon from the sulfuric acid. There is also provided an apparatus for self-heat-extracting flash evaporation of a sulfuric acid alkylation reaction product.