We reported an electrochemical biosensor via CuFe2O4-enhanced photoinitiated chain-growth polymerization for ultrasensitive detection of lung cancer-related gene. In this work, photoinitiated atom transfer radical polymerization (ATRP) was applied to amplify the electrochemical signal corresponding to lung cancer-related gene, and polymerization was triggered off under the illumination of blue light which was involved in copper-mediated reductive quenching cycle. At the same time, CuFe2O4–H2O2 system was also activated to enhance polymerization based on the photocatalysis of CuFe2O4, which was based on the reaction between •OH and methacrylic monomers to generate carbon-based radicals. Numerous ferrocene-based polymer was graft onto electrode surface through this amplification stages. The limit of detection was low to 1.98 aM (in 10 μL, ∼11.9 molecules) (R2 = 0.998) with a wide linear range from 0.1 fM to 10 pM. This strategy made a good trade-off between cost-effectiveness and sensitivity, and it also presented a high selectivity and anti-interference. In addition, the operation was greatly simplified and detection time was also shortened, which endowed this electrochemical DNA biosensor great application potential.