The invention relates to an in-situ combustion development method for an offshore oilfield. The method is characterized in that a horizontal well linear well pattern is adopted as the well-type well pattern, that is, horizontal injection wells and horizontal producing wells are adopted for conducting determinant displacement; and according to determinant displacement, the arrangement relation of the injection wells and the producing wells is that one row of producing wells and one row of injection wells are mutually spaced, and the producing wells correspond to the injection wells. According to the in-situ combustion development method for the offshore oilfield, the horizontal well linear well pattern which is the well-type well pattern suitable for in-situ combustion development of the offshore oilfield is provided, the horizontal injection wells are distributed at the bottom of an oil layer, coke formed through oxidation reaction is majorly formed at the bottom of the oil layer, and adverse factors of air overlapping during regular fire flooding development can be effectively avoided; and an oil drainage function of a fluxible area and an oil drainage function of steam can be better achieved through the horizontal producing wells.