Bloom syndrome helicase (BLM), an important member of RecQ family of DNA helicases, participates in cell metabolism including DNA repair, recombination, transcription, telomere maintenance, and plays key roles in maintaining chromosome stability. The mutation of BLM helicase may lead to Bloom syndrome. Bloom syndrome is a rare autosomal recessive genetic disorder characterized by genomic instability and the early development of many types of cancer. Lomefloxacin (LMX) may treat many diseases by inhibiting many enzymes in cells and interfering DNA metabolism through binding DNA, but the specific mechanism of action remains unclear. This study was conducted to determine the effects of LMX on DNA-binding activity, helicase activity, and ATPase activity of BLM^642～1290 helicase by fluorescence polarized technology and free phosphorus assay technology; and the parameters of binding between LMX and helicase were studied by fluorescence and ultraviolet absorption spectroscopy, included binding constants, number of binding sites, the type of acting force, and binding distance. The results indicated that the reaction between the helicase and LMX was occurred spontaneously, there was one binding site between two molecules, the helicase and LMX might compound BLM-LMX complexes caused by electrostatic force and hydrophobic interaction force; moreover, the intrinsic fluorescence of the helicase was static quenched by LMX as a result of non-radioactive energy transfer. In this process, the helicase and ATPase activities were inhibited and DNA-binding activity of the helicase was promoted by LMX. The mechanism of effects of LMX on biological properties of BLM helicase may be included as below: LMX could inhibit the ATPase activity by allosteric mechanism and stabilize the conformation of the enzyme in low helicase activity state, destroy the coupling of ATP hydrolysis to unwinding, and inhibit the unwinding dsDNA by blocking helicase translocation. The reason that LMX could promote DNA-binding activity of the helicase may be the substitutional functional groups at C-6 and C-7 of LMX which may enhance enzymes activity and strengthen the attachment of drug-enzyme-DNA complex. The results may provide the relative theoretical basis for studying the molecular mechanism of DNA helicase as drug target and understanding the mechanism of action of quinolone drugs.