The invention discloses an apparatus and method to produce isooctane by an indirect alkylation technique. The apparatus comprises fixed-bed reactor I, a catalytic distilling column, an extracting column and a recycling column which are connected in sequence. The method comprises: allowing mixed C4 and a polymerization inhibitor to react in reactor I, feeding part of the product into the catalyticdistilling column, and removing reaction heat from the other part by a heat exchanger before returning; after catalytic distillation, feeding the overhead product into fixed-bed reactor II, reflowingafter reacting, and feeding the bottom product into the extracting column; after extracting, feeding overhead biopolymer into a desulfurizing column, and feeding the bottom product into the recyclingcolumn; after recycling, returning an extracting agent into the extracting column and the polymerization inhibitor to the reactor I; subjecting the biopolymer and hydrogen to hydrodesulfurization in the desulfurizing column to obtain isooctane that may act as a gasoline blend component. Existing MTBE (methyl tert-butyl ether) production equipment is modified into isooctane production equipment; the produced isooctane may act as an ethanol-gasoline blend component; byproducts of the isooctane may also act as other materials for reuse.