The present invention relates to a method for preparing a halogenoacetyl fluoride and the derivatives thereof. The inventive method for preparing a halogenoacetyl fluoride acid is characterized in that said method includes: a step of preparing a halogenoacetyl halide by photo-oxidation of a halogenoethylene compound in conditions such that the transformation rate of the halogenoethylene compound into halogenoacetyl halide is no higher than 80%, producing a reaction mixture essentially including halogenoacetyl halide and the excess halogenoethylene compound; a step of partial fluorination of the mixture obtained by reacting the latter with hydrofluoric acid suitable for obtaining a mixture of halogenoacetyl fluoride and the excess halogenoethylene compound; a step of separating the halogenoacetyl fluoride and the excess halogenoethylene compound. The invention can be used, specifically, for preparing the trichloroacetyl fluoride used as an intermediate species in the production of trifluoroacetic acid.