This is a multi-center, single-arm, open-label, single-dose treatment clinical study to evaluate the safety, tolerability and efficacy of BBM-H803 injection in heavy Hemophilia A subjects. BBM-H803 is an adeno-associated viral (AAV) vector derived from recombinant DNA techniques to contain an expression cassette of the human factor VIII transgene and raises circulating levels of endogenous FVIII.