The invention provides a pyridazinone derivative, and a preparation method and a medical application thereof. O-formylbenzoic acid used as a 
raw material reacts with 
dimethyl phosphite to obtain dimethyl (3-oxo-1,3-dihydroisobenzofuran-1-yl)
phosphonate, the dimethyl (3-oxo-1,3-dihydroisobenzofuran-1-yl)
phosphonate reacts with 3-cyano-4-fluorobenzaldehyde in the presence of 
triethylamine to prepare (Z,E)-2-fluoro-5-[(3-oxoisobenzofuran-1(3H)-ylidene)methyl]
benzonitrile, and the (Z,E)-2-fluoro-5-[(3-oxoisobenzofuran-1(3H)-ylidene)methyl]
benzonitrile is reduced by hydrazine 
hydrate to prepare 2-fluoro-5-[(4-oxo-3,4-dihydropyridazin-1-yl)methyl]
benzoic acid; and 
benzaldehyde or substituted aromatic 
formaldehyde or 
furfural used as a 
raw material and 
malonic acid undergo a Knoevenagel reaction to obtain 
cinnamic acid or substituted 
cinnamic acid or 
furan-2-
acrylic acid, the 
cinnamic acid or substituted cinnamic acid or 
furan-2-
acrylic acid and 1-tert-butoxycarbonylpiperazine undergo an amidation reaction, a tert-butoxycarbonyl group is removed from the obtained amidation product in the presence of 
trifluoroacetic acid, and the obtained product and the 2-fluoro-5-[(4-oxo-3,4-dihydropyridazin-1-yl)methyl]
benzoic acid undergo the amidation reaction to obtain a series of (E)-4-{3-[4-[(3-substituted 
aryl)acryloyl]piperazin-1-carbonyl]-4-fluorobenzyl}-2H-pyridazin-1-one derivatives. Results of preliminary pharmacological activity screening show that the compound represented by a general formula shown in the present invention has a certain in-vitro PARP-1 inhibition ability and a certain in-vitro tumor 
cell proliferation resisting activity. The structural general formula of compound is shown in the description; and in the general formula, Ar is selected from two formulas also shown in the description, and R1, R2, R3, R3, R4 and R5 can be the 
hydrogen atom, the 
fluorine atom, the 
chlorine atom, the 
bromine atom, a 
methyl group, a methoxy group, a tetrafluoromethyl group and a nitro group.