Disclosed in the present invention are a crystal form of a PARP-1 inhibitor and a preparation method therefor. Specifically, disclosed in the present invention are a crystal form A of 4-[[3-[[2-(trifluoromethyl)-5, 6, 7, 8-tetrahydro-[1, 2, 4]triazolo[1, 5-α]pyrazine-7-yl]carbonyl]-4-fluorophenyl]methyl-1(2H)-phthalazinone (formula I) and a preparation method therefor.